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摘要
氮素矿化是决定土壤供氮能力的重要生态过程, 也是目前国内外土壤氮循环研究的重点。养分添加在调节土壤的氮转化方面起着重要的作用。该文以内蒙古锡林河流域温带典型草原为研究对象, 通过不同水平的氮(N)和磷(P)养分添加实验, 利用树脂芯原位培养法分析研究不同水平施氮、施磷对生长季草地土壤氮矿化的影响。结果表明: 高氮处理对草地土壤硝态氮(NO3- -N)、铵态氮(NH4+ -N)及无机氮都有明显的影响, 其中25 g N·m‒2·a‒1和10 g N·m‒2·a‒1高氮处理显著提高了无机氮含量, 25 g N·m‒2·a‒1高氮处理显著增加土壤的NO3- -N及NH4+ -N含量。与施氮相比, 施磷处理对土壤NO3--N、NH4+ -N及无机氮的影响较为有限, 只有12.5 g P2O5·m-2·a-1的磷处理显著促进了NO3- -N及无机氮含量。高氮处理对草地土壤氮素转化有明显影响, 其中25 g N·m‒2·a‒1高氮处理对净硝化速率、氨化速率及矿化速率都有显著的促进作用, 说明高梯度的施氮处理有利于提高土壤的供氮能力。氮是内蒙古锡林河流域草原生态系统有机氮矿化的限制因子。与施氮相比, 施磷处理对草地土壤氮转化的作用较为有限, 仅有12.5 g P2O5·m-2·a-1 + 2 g N·m‒2·a‒1处理显著促进生长季中期的净氨化速率。说明施磷对土壤氮转化的影响弱于施氮的影响。养分添加显著提高了草地的地上生物量。 养分添加情景下, 土壤湿度与净矿化速率极显著相关, 表明湿度是影响该区域温带草原土壤氮矿化的主效因素。环境因子(如有机碳含量、土壤全氮及土壤C/N)与不同氮处理下的净矿化速率之间显著相关, 而土壤微生物碳、氮含量与土壤氮矿化均没有显著相关性。
关键词：
Abstract
Nitrogen (N) mineralization is an important ecological process which determines soil N supplying ability, and it is a key research domain of soil N cycling worldwide at present. Nutrient addition can play a key role in regulating soil N transformations. The objective of the study was to evaluate the effects of different levels of N and P additions on in situ N mineralization during growing seasons in the temperate grasslands.
We conducted an field N and P fertilization addition experiment in the temperate grassland in Nei Mongol in June 2014. Five levels of N (0-25 g N·m‒2·a‒1), five levels of P (0-12.5 g P2O5·m-2·a-1) addition treatments, and a control were set up. We measured the in situ net mineralization rate, ammonification rate, and nitrification rate using the resin core incubation technique once a month from July to October 2014. Aboveground biomass and some selected soil chemical and microbial properties were also measured in the study.
High nitrogen addition did significantly affect the contents of inorganic N. High N addition levels (25 g N·m‒2·a‒1 + 1 g P2O5·m-2·a-1 and 10 g N·m‒2·a‒1 + 1 g P2O5·m-2·a-1) significantly increased soil inorganic N content, and the 25 g N·m‒2·a‒1 + 1 g P2O5·m-2·a-1 treatment markedly increased soil nitrate- (NO3- -N) and ammonium-N (NH4+ -N). Compared to N addition, P addition had limited effects on soil inorganic N, NO3- -N and NH4+ -N. Only the 12.5 g P2O5·m-2·a-1 + 2 g N·m‒2·a‒1 treatment significantly increased soil ammonium-N and inorganic N. N addition did significantly affect microbial N transformation rates. The 25 g N·m‒2·a‒1 + 1 g P2O5·m-2·a-1 treatment significantly stimulated soil net N nitrification rate, mineralization rate and ammonification rate, suggesting that high N addition can effectively improve soil available N supply. N was a limiting factor to soil organic N mineralization in the study area. P addition had negligible effects on soil net N mineralization and nitrification rates, and only the 12.5 g P2O5·m-2·a-1 + 2 g N·m‒2·a‒1 treatment significantly enhanced ammonification rate in the middle of growing season. The results also indicated that impacts of P addition on soil N mineralization were weaker than impacts of N. Moreover, N and P addition significantly increased aboveground biomass. Under the N and P addition, soil moisture was significantly correlated with net mineralization and nitrification rate, which suggested that it was one of the dominant factors affecting N. Net N mineralization and nitrification rate under N fertilization was significantly correlated with environmental factors (soil organic C, soil C/N and soil total N). Soil N mineralization was not positively correlated with the soil microbial biomass N or C.
Keywords：
氮和磷是陆地生态系统限制生长的关键养分因子, 对植物的生长有十分重要的作用, 影响着生态系统的生产力和生态过程(Elser et al., 2007; Vitousek et al., 2010)。 土壤氮矿化是土壤有机态氮在微生物作用下转化为无机态氮的过程, 是保持土壤氮可利用性的主要方式, 也是生态系统氮循环的重要环节(Abera et al., 2012)。因此, 对土壤氮矿化的动力学机制的理解非常必要。微生物是土壤氮转化的主体, 由微生物驱动的氮转化过程包括生物固氮作用、硝化作用、反硝化作用和氨化作用等(Holst et al., 2007; Müller et al., 2007), 并受到生物与非生物因子(如土壤温度、湿度、有机质及微生物群落结构等)的影响(Zaman & Chang, 2004; Liu et al., 2010)。养分添加在调节土壤的氮转化方面起着重要的作用(Zhang et al., 2012)。草地养分添加是提高草地生态系统生产力的有效策略, 添加养分(如氮、磷)能增加土壤无机氮库, 同时可激发土壤有机质的分解(Köchy & Wilson, 2001; 张璐等, 2009; Wang et al., 2014)。目前, 氮添加对草地土壤氮矿化影响方面的研究已取得一定进展, 其研究结果因土壤养分含量、气候类型、施氮时间尺度长短及其剂量或类型的不同而有所差异(Aggangan et al., 1998; 刘碧荣等, 2015)。一般情况下, 氮添加对土壤有机氮的矿化及硝化速率具有促进作用。但是,一些研究表明氮素添加对土壤矿化没有明显影响, 或对其具有负面作用(Emmett et al., 1998; Jussy et al., 2004; Wang et al., 2014; Ma et al., 2011)。磷是草地生态系统植物生长和重要生态过程的主要限制因子, 在养分循环中具有一定的调控作用(Vance et al., 2003)。磷添加直接影响着草地土壤无机氮的形式、浓度以及氮矿化过程, 是影响氮矿化作用的重要因子(Li et al., 2010; Wang et al., 2014)。 尽管国内外有关氮添加与草地土壤矿化这一领域的研究较多, 但关于草地土壤净矿化作用对磷添加的响应方面的研究仍非常有限(Wang et al., 2014), 其深入的机制仍不甚清楚, 这方面的研究鲜见报道。地处欧亚大陆温带干旱、半干旱区的内蒙古草原是我国北方温带草原的主体, 储存了大量的土壤碳, 在我国草地碳氮平衡中具有重要地位(朴世龙等, 2004)。20世纪60年代以来, 因农业用地增加、大陆性干旱气候因素及大规模放牧的影响, 内蒙古区域温带半干旱草原退化较严重, 并且其生态系统维持较低的土壤氮、磷养分水平(Hooper & Johnson, 1999; Cao et al., 2004; 乌恩等, 2006; Zhang & Han, 2008)。近几十年来, 随着化肥的使用及大气氮沉降的增加, 草地生态系统的养分水平不断增加, 我国草地生态系统仍面临较高的氮沉降量(Lü & Tian, 2007; Yang et al., 2012)。虽然近年来关于半干旱区草地土壤氮矿化对氮添加的响应方面已有一定的研究, 但仅限于室内培养条件(张璐等, 2009; Liu et al., 2015)。室内培养与自然生态系统的氮矿化相比有一定局限性。而树脂芯方法通过野外原位培养, 能较好地反映土壤氮的实际氮矿化速率(Bhogal et al., 1999)。基于以往研究的问题和局限性, 本研究以内蒙古温带典型草原为研究对象, 通过在生长季的野外树脂芯原位培养观测, 了解不同氮、磷添加水平对我国内蒙古温带典型草原土壤无机氮含量的影响, 探讨不同水平氮、磷添加对土壤氮净矿化、硝化及氨化速率的影响, 并结合环境和生物因子, 分析其与土壤氮矿化的关系, 认识养分水平增加以及协同有关环境及生物因子对内蒙古温带草原土壤氮转化的影响效应。
该实验在中国内蒙古锡林浩特内蒙古大学毛登牧场生态实验站(116.03°‒116.50° E, 44.80°‒44.82° N)开展。 此地气候属于温带大陆性气候, 年平均气温0‒1 ℃, 年积温1800 ℃, 年降水量300-360 mm, 降水多集中在6‒8月, 无霜期90‒115天, 具有光、热、水同期的特点。土壤以栗钙土为主, 有少量褐色土, 栗钙土层15‒80 cm, 土质比较肥沃。植被群落以大针茅(Stipa grandis)和羊草(Leymus chinensis)为主。
氮添加试验设置6个水平处理, 分别为对照(CK, 未添加氮素和磷素)、N1 (0 g N·m‒2·a‒1 + 1 g P2O5·m‒2·a‒1)、N2 (2 g N·m‒2·a‒1 + 1 g P2O5·m‒2·a‒1)、N3 (5 g N·m‒2·a‒1 + 1 g P2O5·m‒2·a‒1)、N4 (10 g N·m‒2·a‒1 + 1 g P2O5·m‒2·a‒1)和N5 (25 g N·m‒2·a‒1 + 1 g P2O5·m‒2·a‒1) , 其设置依据Liu等(2013)文献。每个处理3次重复, 共计18个实验小区(面积为 6 m × 6 m)。氮肥为硝酸铵(NH4NO3)。为确保不受磷限制, 除对照外, 各处理小区添加一定量的磷素(1 g P2O5·m‒2)。
磷添加设置为对照(CK, 未添加氮素和磷素)、P1 (0 g P2O5·m‒2·a‒1 + 2 g N·m‒2·a‒1)、P2 (1 g P2O5· m‒2·a‒1 + 2 g N·m‒2·a‒1)、P3 (2.5 g P2O5·m‒2·a‒1 + 2 g N·m‒2·a‒1)、P4 (5 g P2O5·m‒2·a‒1 + 2 g N·m‒2·a‒1)和P5 (12.5 g P2O5·m‒2·a‒1 + 2 g N·m‒2·a‒1) 6个水平处理, 磷肥为NaH2PO4。除对照外, 每个小区都添加一定量的氮素(2 g N·m‒2)。每个水平3个重复; 共计18个小区。所有小区和处理都随机排列。相邻小区之间设置1 m的缓冲带。2014年6月一次性均匀喷施。
利用树脂芯方法(Bhogal et al., 1999)对生长季的土壤净氮矿化情况进行测定。实验自2014年7月15日开始, 在各小区随机选择具有代表性的样点, 齐地面剪去地上植被后, 用PVC管(内径8 cm, 高12 cm)取4管0‒10 cm土层的土, 装入1个自封袋内混匀, 用于测定NH4+ -N和NO3- -N的初始值。垂直安装PVC管, 然后将管取出, 去除底部2 cm的土壤后, 依次放入滤纸、阴离子交换树脂袋、滤纸、石膏垫, 最后将PVC管埋入原处进行野外定位培养。试验于2014年7月15日埋入第1批培养管, 以后每隔30天取回上次埋入的培养管, 再置新管, 直至2014年10月15日结束。土壤样品采集后, 立即低温保存, 用于测定无机氮(矿质氮)的浓度。
NH4+-N含量利用传统的浸提-靛酚兰比色法(郑必昭, 2013)测定, NO3--N含量采用紫外分光光度法(郑必昭, 2013)测定, 阴离子交换树脂所吸附淋溶的NO3--N采用双波段分光光度法(郑必昭, 2013)测定。根据培养前后土壤无机氮含量之差, 分别计算土壤氮素的净硝化速率、净氨化速率和净氮矿化速率等指标(Liu et al., 2010), 具体公式如下。
RM = (NAA + NAN + NE) - (NBA + NBN ) / T (1)
RA = (NAA - NBA) / T (2)
RN = (NAN + NE - NBN) / T (3)
式中, NBA为培养前的NH4+-N量; NBN为培养前的NO3--N含量; NE为淋溶硝氮含量; NAA为培养后的NH4+-N量; NAN为培养后的NO3--N含量; RM为净矿化速率; RA为净氨化速率; RN为净硝化速率; T为培养时间。
利用土壤温度和土壤水分传感器在每一个培养时期测定15 cm深度的土壤温度和湿度。2014年8月中旬, 在每个小区内按Z字形选取5个采样点, 去除采样点地表的植被, 用内径5 cm的土钻分3层(0-10、10-20和20-30 cm)取土壤样品, 每一采样点的不同层次样品混匀后装入塑料封袋中, 将5袋土样带回实验室。一部分用于土壤理化性质的测定, 另一部分置于‒20 ℃冰箱保存, 用于土壤微生物生物量测定。土壤有机质测定采用重铬酸钾氧化-外加热法(Nelson & Sommers, 1996); 土壤全碳、全氮利用基于元素分析仪(Vario MAX CN, Elementar, Hanau, Germany)的杜马斯催化燃烧法(Chatterjee et al., 2009)测定。土壤微生物量碳和氮利用氯仿熏蒸浸提法(Vance et al., 1987)进行测定。
2014年8月中旬, 在植物生长高峰期, 在不同水平氮、磷添加处理下的每块样地中选择3个1 m × 1 m的样方进行群落生物量调查, 齐地面剪取样方地上部分, 带回实验室在70 ℃下烘干至恒质量。
运用SPSS 13.0软件对数据进行分析, 利用一般线性模型对整个试验期间各氮或磷添加处理的土壤NO3--N和NH4+-N含量、无机氮含量、净硝化和氨化速率以及净矿化速率进行重复测量方差分析; 并对每个月各施氮、磷水平处理的各指标进行单因素方差分析(one-way ANOVA), 采用最小显著差数法(least significant difference, LSD)进行多重比较。统计显著水平均为α = 0.05。利用Pearson相关分析了解草地净硝化速率、净氨化速率和净矿化速率与影响因子的相关关系。
在整个试验期间, 6种不同施氮处理之间的土壤NO3--N含量存在显著差异(p < 0.05)。相比于CK, N5处理显著增加了NO3--N浓度(p < 0.05)。各施氮处理的NO3--N含量存在相似的季节内变化(图1A), 从7月至8月缓慢上升, 并在8月达到最大值, 而9月和7月较小。不同氮处理下的NO3- -N含量的变化范围为10.40‒53.45 mg·kg-1。
在整个试验期间, 不同施氮处理之间的NH4+-N含量呈现边缘显著差异(p = 0.083)。相比于CK, 处理N5显著增加了NH4+-N含量(p < 0.05)。各施氮处理的NH4+-N存在相似的季节内变化, 其含量随着培养期间的延长而逐渐增加(图1B)。在整个实验时期, 与CK相比, N1、N2、N3、N4及N5的NH4+-N含量分别提高了6.1%、38.34%、7.40%、25.46%及113%。不同氮处理下NH4+-N含量的变化范围为0.90‒6.24 mg·kg-1。经过氮添加及原位培养后, 施氮处理和对照的NO3--N含量都大于NH4+-N, 仍是土壤无机氮的主要存在形式。
在整个生长季, 不同施氮处理之间的无机氮含量存在显著差异(p < 0.05), 与CK相比, N4和N5显著增加了土壤的无机氮含量(p < 0.05)。各施氮处理的无机氮存在相似的季节内变化(图1C), 其含量在8月达到最高峰。
图1 不同氮处理下的土壤NO3--N (A)、NH4+-N (B)及无机氮含量(C)的时间变化(平均值±标准偏差, n = 3)。竖线表示不同氮处理间的差异显著性(p < 0.05)。CK, 对照, 未添加氮素和磷素。N1、N2、N3、N4、N5分别添加氮素0、2、5、10、25 g N·m‒2·a‒1, 添加磷素1 g P2O5·m‒2·a‒1。
Fig. 1 Temporal variations of soil NO3--N (A), NH4+-N (B) and soil inorganic N concentration (C) under different N treatments (mean ± SD, n = 3). The vertical line denotes the least significant difference among different N treatments (p < 0.05). CK, control, without nitrogen and phosphorus. N1, N2, N3, N4, N5 add nitrogen 0, 2, 5, 10, 25 g N·m‒2·a‒1, respectively. Other than in the control, 1 g P2O5·m‒2·a‒1 is added to each treatment.
在整个试验时期, 不同施磷处理之间的NO3--N含量差异边缘显著(p = 0.061); 相比于CK, P5 (12.5 g P2O5·m‒2·a‒1)处理显著增加了NO3--N浓度(p < 0.05)。不同施磷处理的NO3- -N含量存在相似的季节内变化模式, 从7月至8月逐渐上升, 并在8月达到最大值, 而9月份为最小值(图2A)。不同施磷处理下NO3--N含量的变化范围是7.70‒47.60 mg·kg -1。在整个生长季节, NH4+-N含量在不同磷处理之间未呈现显著差异, 磷添加并未显著影响NH4+-N浓度(p > 0.05)。在整个实验期间, P5处理的平均NH4+-N含量最大, 略高于CK, 二者的比例为1.27。不同磷处理的NH4+-N存在一定的季节内波动, 但处理间变化格局并不相似(图2B); 总体上, 各处理NH4+-N都随着实验时间的延长而逐渐增加, 而10月份的NH4+-N略有变小, 其变化范围为0.77‒6.85 mg·kg-1。此外, 在整个培养期间, 5种施磷处理下的平均土壤无机氮含量均高于CK, 其中P5处理的无机氮含量为CK的1.25倍(p < 0.05)。
图2 不同磷处理下的土壤NO3- -N (A)、NH4+ -N (B)及无机氮含量(C)的时间变化(平均值±标准偏差, n = 3)。竖线表示不同磷处理间的差异显著性(p < 0.05)。CK, 对照, 未添加氮素和磷素。P1、P2、P3、P4、P5分别添加磷素0、1、2.5、5、12.5 g P2O5·m‒2·a‒1, 添加氮素2 g N·m‒2·a‒1。
Fig. 2 Temporal variations of soil NO3--N (A), NH4+-N (B) and soil inorganic N concentration (C) under different P treatments (mean ± SD, n = 3). The vertical line denotes the least significant difference among different P treatments (p < 0.05). CK, control, without nitrogen and phosphorus. P1, P2, P3, P4, P5 add phosphorus 0, 1, 2.5, 5, 12.5 g P2O5·m‒2·a‒1, respectively. Other than in the control, 2 g N·m‒2·a‒1 is added to each treatment.
在整个试验期间, 处理N1、N2、N3及N4并未显著影响净硝化速率, 但处理N5显著增加了净硝化速率(p < 0.05)。不同施氮处理的净硝化速率动态变化如图3A所示。实验初期(7月至8月)各氮处理的净硝化速率最高, 实验中期(8月至9月)的净硝化速率出现负值, 而至实验末期(9月至10月)时的净硝化速率有所回升。各施氮处理下净硝化速率的变化范围为‒0.67-1.22 mg·kg-1·d -1。
在整个生长季节, 净氨化速率在不同氮处理之间存在显著的差异(p < 0.05)。相比于CK, N5处理显著增加了净氨化速率(p < 0.05)。 施氮处理下的净氨化速率存在明显的季节内变异格局(图3B), 8月至9月达到高峰。N5和CK处理的平均净氨化速率为0.083和0.026 mg·kg-1·d -1。
图3 不同氮处理下, 不同时间段的净硝化速率(A)、氨化速率(B)及矿化速率(C) (平均值±标准偏差, n = 3)。不同字母代表差异显著(p < 0.05)。n.s.表示处理间差异不显著。处理同
Fig. 3 Soil net N nitrification (A), ammonification rates (B) and mineralization rates (C) in different periods under different N treatments (mean ± SD, n = 3). Different lowercase letters represent significant differences at p < 0.05. Non-significant differences are indicated by n.s. Treatment see
在整个培养时期内, 净矿化速率在不同氮处理之间存在边缘显著差异(p = 0.08)。相比于CK, 处理N5显著增加了净矿化速率(p < 0.05)。氮处理下净矿化速率的动态变化如图3C所示, 并与硝化速率的变化相似。不同施氮处理下的净矿化速率变化范围为-0.58-1.24 mg·kg-1·d -1。
在整个试验期间, 净硝化速率在不同磷处理之间未达到显著水平。方差分析表明, 相比于CK, 其他5种施磷处理并未显著提高净硝化速率。不同磷处理下的净硝化速率均表现出季节内变化波动, 并且各处理的变化趋势基本一致(图4A); 其中, 8月至9月的净硝化速率出现负值。各施磷处理下净硝化速率的变化范围是-1.12-1.08 mg·kg-1·d -1。
在整个培养期间, 6种施磷处理的净氨化速率不存在显著差异。但在8月至9月, P5处理的净氨化速率显著高于CK (p < 0.05)。由图4B还可看出, 不同磷处理下的净氨化速率存在明显的季节内变化模式, 生长季中期(8月15日至9月15日)达到最高峰, 而进入生长季末期(9月15日至10月15日)后降低。
图4 不同磷处理下, 不同时间段的净硝化速率(A)、氨化速率(B)及净矿化速率(C) (平均值±标准偏差, n = 3)。同一培养时期比较, 不同字母代表差异显著(p < 0.05)。n.s.表示处理间差异不显著。处理同
Fig. 4 Soil net N nitrification (A), ammonification rates (B) and mineralization rates (C) in different periods under different P treatments (mean ± SD, n = 3). Different lowercase letters represent significant differences at p < 0.05. Non-significant differences are indicated by n.s. Treatment see
在整个生长季节, 净矿化速率在不同施磷处理之间并未达到显著水平。不同施磷处理的净氮矿化速率的动态变化如图4C所示, 其中8月至9月的净氮矿化速率出现负值(表示培养后的值低于初始值), 并为整个实验期间的最低值。
氮添加显著提高了草地的地上生物量(p < 0.05)(图5A), 其中以N4最为明显。 地上生物量在不同磷处理间存在显著差异(p < 0.05), 与对照相比, P4、P3及P2显著提高了地上生物量(p < 0.05)(图5B)。
图5 2014年8月份不同氮(A)、磷处理(B)下的地上生物量(平均值±标准偏差, n = 3)。不同字母分别表示处理间差异显著(p < 0.05)。CK, 对照, 未添加氮素和磷素。N1、N2、N3、N4、N5分别添加氮素0、2、5、10、25 g N·m‒2·a‒1, 添加磷素1 g P2O5·m‒2·a‒1。 P1、P2、P3、P4、P5分别添加磷素0、1、2.5、5、12.5 g P2O5·m‒2·a‒1, 添加氮素2 g N·m‒2·a‒1。
Fig. 5 The aboveground biomass under different N (A) and P addition treatments (B) in August of 2014 (mean ± SD, n = 3). Different lowercase letters represent significant differences at p < 0.05. CK, control, without nitrogen and phosphorus. N1, N2, N3, N4, N5 add nitrogen 0, 2, 5, 10, 25 g N·m‒2·a‒1, respectively. P1, P2, P3, P4, P5 add phosphorus 0, 1, 2.5, 5, 12.5 g P2O5·m‒2·a‒1, respectively. Other than in the control, 1 g P2O5·m‒2·a‒1 is added to each treatment in the N addition experiment, and 2 g N·m‒2·a‒1 is added to each treatment in the P addition experiment.
氮添加条件下土壤净矿化速率随土壤湿度的增加而升高, 净氮矿化速率和硝化速率与土壤湿度均极显著正相关(p < 0.001)(表1)。而土壤温度与净氮矿化及硝化速率间的相关性不显著, 与氨化速率之间的正相关性明显(p < 0.05)。土壤有机碳、土壤全氮与净矿化及硝化速率显著正相关, 土壤碳氮比(C/N)与净矿化、硝化速率存在显著负相关关系(p < 0.05), 而土壤微生物碳氮与土壤氮转化过程均未呈现显著的相关关系。
表1 不同氮处理下的净矿化、硝化及氨化速率与环境及生物因子之间的相关性
Table 1 Correlation between environmental/biological factors and net N mineralization, nitrification, and ammonification rates under different N addition treatments
| 环境及生物因子 Environment/biological factor | 净矿化速率 Mineralization (mg·kg-1·d -1) | 净硝化速率 Nitrification (mg·kg-1·d-1) | 净氨化速率 Ammonification (mg·kg-1·d-1) |
|---|---|---|---|
| 土壤湿度 Soil moisture (V/V) | 0.825*** | 0.813*** | 0.323 |
| 土壤温度 Soil temperature (℃) | 0.142 | 0.114 | 0.245* |
| 土壤有机碳 Soil organic C (g·kg-1) | 0.887* | 0.879* | 0.418 |
| 土壤全氮 Soil total N (%) | 0.848* | 0.830* | 0.612 |
| 土壤碳氮比 Soil C:N ratio | 0.849* | 0.858* | 0.014 |
| 微生物碳 Microbial biomass C (mg·kg-1) | 0.422 | 0.410 | 0.396 |
| 微生物氮 Microbial biomass N (mg·kg-1) | 0.298 | 0.266 | 0.791 |
磷添加情境下的土壤净矿化速率随土壤湿度的增加而增加, 净氮矿化速率和硝化速率与土壤湿度均极显著正相关(p < 0.01)(表2)。而土壤温度与净氮矿化及硝化速率间的相关性不显著, 与氨化速率之间的正相关性明显(p < 0.01)。土壤有机碳、土壤全氮、土壤碳氮比(C/N)、土壤微生物碳氮与净矿化、氨化及硝化速率之间均未呈显著的相关关系。
表2 不同磷处理下的净矿化、硝化及氨化速率与环境及生物因子之间的相关性
Table 2 Correlation between environmental/biological factors and net N mineralization, nitrification, and ammonification rates under various P addition treatments
| 环境及生物因子 Environment/biological factor | 矿化速率 Mineralization (mg·kg-1·d-1) | 硝化速率 Nitrification (mg·kg-1·d-1) | 氨化速率 Ammonification (mg·kg-1·d-1) |
|---|---|---|---|
| 土壤湿度 Soil moisture (V/V) | 0.730*** | 0.673** | 0.10 |
| 土壤温度 Soil temperature (℃) | 0.246 | 0.326 | 0.725** |
| 土壤有机碳 Soil organic C (g·kg-1) | 0.527 | 0.626 | 0.601 |
| 土壤全氮 Soil total N (%) | 0.372 | 0.544 | 0.662 |
| 土壤碳氮比 Soil C:N ratio | 0.573 | 0.292 | 0.251 |
| 微生物碳 Microbial biomass C (mg·kg-1) | 0.269 | 0.308 | 0.280 |
| 微生物氮 Microbial biomass N (mg·kg-1) | 0.391 | 0.511 | 0.556 |
土壤NH4+-N和NO3--N是无机氮的主要存在形式, 也是植物从土壤中吸收氮素的主要形态。研究草地土壤无机氮动态及其影响因素对于了解草原生产力、氮素循环与转化具有重要的意义(Zhang et al., 2012; Liu et al., 2015)。草地土壤无机氮含量取决于无机氮素的输入(如氮添加和土壤净氮矿化)和植物吸收和利用之间的平衡(Zhang et al., 2012; 刘碧荣等, 2015; Liu et al., 2015)。在本研究中, 随着氮添加浓度的增加, 土壤NO3--N和NH4+-N含量有所增加, 其中高氮处理N5显著增加了土壤的无机氮浓度。 这主要是因为施肥提高了土壤有效氮水平, 同时对土壤氮素矿化作用、硝化作用也有一定的正面影响, 进而提高了土壤无机氮及铵态氮、硝态氮的含量(包翔等, 2015; Wang et al., 2015)。此外, 氮添加处理显著增加了草地的生物量, 其中高氮处理的效果较为明显, 反映了氮是限制内蒙古锡林河流域植物生长的决定因子(Zhang et al., 2012)。受氮限制的草地生态系统能够很好地固定外源氮, 并且有能力吸收利用足够的外源氮, 从而提高了生态系统的生产力和生物量(Liu et al., 2015)。在高氮添加情景下, 通过植物生长吸收利用的矿质氮含量并不能掩盖高氮输入对土壤无机氮的显著影响。
磷处理P5对NO3--N及无机氮含量都表现出显著的促进作用, 高剂量的磷输入引起草地土壤无机氮及其组分含量的显著增加。目前, 关于草地土壤矿质氮对磷添加的响应方面的研究较少(Wang et al., 2014), 有关的机理还未形成一致的结论。在黄土高原典型草原的结果显示, 磷添加在一定程度上降低了草地土壤无机氮库(Wang et al., 2014), 本研究结果与之有所差异。土壤异养微生物活性在调控土壤无机氮含量中起决定性的作用(White & Reddy, 2000; Pandey & Begum, 2010)。高磷输入可能提高了草地土壤异养微生物(如参与硝化反应的异养硝化细菌)的活性, 并由此增加了净氮矿化速率, 进而提高了土壤NO3--N及矿质氮的含量。此外, 高磷输入也可能减弱了土壤微生物对无机氮的固持作用, 从而增加了无机氮的浓度(White & Reddy, 2000; Chapin et al., 2002), 但其深入的机制仍需要进一步的研究。
氮素添加显著改变了土壤的累积氮矿化量, 并对土壤氨化、硝化及矿化速率具有明显的促进作用(Loiseau & Soussana, 2000; Li et al., 2006; Vourlitis & Zorba, 2007; Wang et al., 2015)。高氮处理N5明显促进了草地的净硝化、净氨化及净矿化速率。 Gundersen等(1998)提出在氮限制的生态系统中, 氮输入对净矿化作用具有促进效应。本研究的生物量结果表明, 氮是本研究区草原生态系统主要的限制元素。氮肥输入后通过增加土壤养分、土壤易矿化的有机氮水平以及土壤微生物活性及生物量, 进而直接影响了土壤氮矿化过程(Aggangan et al., 1998; Delin & Linden, 2002; Kadono et al., 2008)。本研究中, 低氮处理对草地土壤氮素净矿化速率的促进作用并不显著。本实验在6月中旬添加氮素, 而布置PVC培养管是在7月中旬以后(并且埋入深度仅有12 cm), 由此可推测: 土壤表层NO3--N会随夏季降雨淋溶而向下层迁移, 并造成矿质氮含量的下降, 这可能是导致低氮添加对矿质氮含量和氮转化过程没有显著影响的一个原因(任艳林, 2012)。氮矿化过程受多种生物因子和非生物因素的影响, 并以土壤有机质、温度及土壤水分有效性等最为重要(Chapin et al., 2002; Zaman & Chang, 2004; Liu et al., 2010; Ma et al., 2011)。氮添加情景下的净矿化、硝化速率与土壤有机碳和土壤全氮之间呈显著的正相关关系, 表明了土壤有机碳及全氮的增加对草地土壤矿化及硝化作用都具有明显的促进效应(Hacin et al., 2001; Wang et al., 2008; Zhang et al., 2008)。土壤中较高的有机碳和全氮含量提高了微生物的活性, 进而促进了氮素矿化速率(Berendse, 1990; Kitayama, 1996; Sanchez et al., 1997)。净矿化及硝化速率与土壤C/N之间呈显著的负相关关系, 进一步反映了氮添加会降低温带典型草原土壤的C/N, 引起碳的有效性减少及微生物对N需求的下降, 从而促进了土壤净氮矿化速率(Hart et al., 1994; Vourlitis & Zorba, 2007; Ma et al., 2011)。土壤微生物量氮、碳与净矿化和硝化速率之间并不存在显著的相关性, 以往的研究也得出类似的结果(Holems & Zak, 1994; Hossain et al., 1995; Bengtsson et al., 2003; 傅民杰等, 2009), 说明土壤微生物碳氮量对草地土壤氮矿化的影响十分有限(Puri & Ashman, 1998)。这可能是因为土壤氮矿化作用受到土壤微生物量及微生物活性的共同影响, 并且微生物活性比微生物生物量更能促进氮素的矿化(Hassink et al., 1993)。本试验并未涉及微生物活性的测定, 微生物活性在氮矿化过程中的功能及作用仍需做进一步分析, 建议今后在研究土壤微生物对土壤有机氮矿化过程时应充分考虑其活性的效应。
磷是草地生态系统植物生长和重要生态过程的主要限制因子, 在养分循环中具有一定的调控作用(Vance et al., 2003; Dodd et al., 2014; Wang et al., 2014)。内蒙古天然草地土壤处于低磷或缺磷状态, 尤其是在退化区域(乌恩等, 2006)。近年的实验证实, 半干旱沙质草地土壤氮矿化及硝化作用并不受外源磷添加的影响(Li et al., 2010)。已有的研究显示, 森林生态系统中的土壤净硝化速率因其土壤有效磷的不同而有所差异(Pastor et al., 1984)。Aggangan等(1998)的研究显示, 施磷并不对种植园土壤的净矿化速率产生影响。 本研究中, 磷输入显著提高了草地的地上生物量, 表明该草地生态系统受磷的明显限制。 磷添加的土壤净硝化速率及矿化速率与对照相比并没有显著提高, 但高磷处理(P5)显著增加了净氨化速率, 反映了施磷处理对草地土壤净氨化速率的影响更为显著。 此结果进一步说明, 磷添加对土壤氮素转化作用的影响弱于氮添加的影响。尽管较高梯度的磷处理能够显著增加NO3--N和无机氮浓度, 但净矿化及硝化速率对施磷量的增加未有显著响应, 高磷输入未显著促进土壤微生物氮转化的关键过程。这主要是因为土壤微生物吸收和固定了大量新形成的NO3--N, 限制了净硝化速率的提高(Sahrawat et al., 1985; Minick et al., 2011)。微生物固持土壤矿质氮的比例取决于土壤微生物体氮的周转以及随后的微生物体氮的稳定性(Fisk & Fahey, 2001; Miltner et al., 2009)。另外一方面可能是因为所施加磷的剂量及短期的磷处理时间对草地氮素净矿化量并不具有显著的促进作用。 因此, 本研究的磷浓度添加处理和短期的处理时间还不能完全反映磷添加对土壤氮矿化的整体影响。若要进一步验证草地生态系统土壤氮素转化关键过程对磷输入增加的响应, 还需要进行长期的、高剂量磷素的野外定位观测, 以进一步揭示草地土壤氮素净矿化量特征及其影响机理。磷添加能够改变土壤的生物、非生物特性以及有机质质量, 进而对土壤氮循环过程产生显著影响(Wang et al., 2014)。但本结果显示, 不同施磷处理下的草地土壤有机碳、全氮、碳氮比及微生物生物量与净氮矿化速率间均不存在显著相关性。因此, 这些环境及生物因子并不能很好地预测本地磷添加情景下的草地土壤氮素矿化格局, 其具体原因有待更深入的研究。
氮磷添加情景下的净矿化速率呈明显的季节内动态变化格局。土壤氮矿化的动态变化受多种因素的影响, 其中土壤水分和温度的季节变化可以直接促进或抑制氮素转化(Pandey et al., 2007; Liu et al., 2010)。在生长季中期(8-9月), 草地土壤的净矿化速率仍出现负值, 说明土壤无机氮向有机氮转化, 系统净消耗无机氮。这可能与此期间土壤净矿化和硝化作用与生物固持的相对强弱有关(孙志高和刘景双, 2007; Liu et al., 2010)。值得注意的是, 在培养末期(9-10月), 低氮处理可以促进氮矿化作用, 而高氮处理(N5)下的净氮矿化速率小于低氮处理和对照, 反而在一定程度上抑制了土壤氮矿化, Aggangan等(1998)和张璐等(2009)也得出类似的结果, 表明土壤净氮矿化速率并不与氮输入量增加正相关, 当氮输入量达到一定水平后, 氮矿化速率会下降(Aber & Magill, 2004)。另外, 每一个培养时期的表层土壤(0-12 cm)中的初始无机氮及其组分的含量都存在差异, 其中第三次培养时期(9月15日-10月15日)的表层土壤无机氮含量初始值较高, 土壤中较高的矿质氮初始值限制了土壤氮矿化, 对氮矿化过程具有负面影响(Sierra, 1992; Aggangan et al., 1998)。在整个培养过程中, 草地的净矿化速率最大值出现在7-8月, 这主要与土壤水分状况有关。在这一时期, 土壤湿度几乎是最高的, 再加上适宜的温度, 较好的水热条件, 使得微生物活性与生长较强, 并促进了土壤氮矿化作用(Zhang et al., 2012; 邹亚丽等, 2014)。养分添加情境下的土壤净矿化速率和硝化速率与土壤湿度呈显著正相关关系, 但土壤温度对氮矿化及硝化速率等土壤氮循环关键过程并无显著影响。因此, 在植物生长季内, 温度不是制约草地土壤氮转化的主要影响因子。 本试验区域处在半干旱气候带, 土壤水分长期维持较低的水平, 特别是干旱年土壤含水量更低。以往的研究显示, 土壤含水量在低于15%时对土壤净氮矿化起限制作用(Dalias et al., 2002); 土壤温度在5‒35 ℃时, 土壤净矿化速率随着温度的增加而增加(Wang et al., 2006)。本实验中, 土壤含水量在整个生长季培养期内多小于15%, 而土壤温度在5-24 ℃之间波动。因此, 尽管生长季内土壤温度条件适宜土壤有机质的矿化, 但由于较低土壤水分的限制作用, 降低了本应随温度增加的土壤净矿化量, 使得土壤水分对土壤氮矿化作用的影响更为显著, 成为影响净氮矿化速率变化的主要制约因子(董云社等, 2005; Liu et al., 2015)。
在氮磷养分添加情境下, 内蒙古锡林河流域温带典型草原生长季土壤氮矿化过程以硝化作用为主, 说明了NH4+-N向NO3--N转变, 以满足植物生长利用需求, NO3- -N是形成草地地上植被生物量的有效氮素, 这与邹亚丽等(2014)和Zhang等(2012)的结论类同, 但与Holub和Záhora (2008)的研究结果有一定差异, 其结果显示微生物氮转化形成的土壤 NH4+-N含量大约为NO3--N含量的3倍, 这与本试验的结果区别很大。
高氮处理对内蒙古温带草原土壤氮素转化有明显影响, 其中高氮处理(N5和N4)显著增加了土壤中的无机氮库, 并且处理N5显著增强净硝化、氨化及矿化速率, 促进了土壤微生物氮转化, 表明氮是该草原生态系统有机氮矿化的限制因子。添加高剂量的氮素(25 g N·m‒2·a‒1)有利于增加草地植被生产力, 增强有机氮的矿化能力, 有利于该区域草地的可持续性利用。 与施氮相比, 施磷处理对草地土壤氮转化过程的影响十分有限, 说明内蒙古锡林河流域草地土壤有机氮的矿化可能不受磷的限制。 本研究添加的磷浓度和短期的磷处理时间还不能完全反映磷的添加对土壤氮矿化的整体影响。若要进一步验证草地生态系统土壤氮素转化关键过程对磷输入增加的响应, 还需要进行长期的、高剂量磷素的野外定位观测, 以揭示草地土壤氮素净矿化量特征及其影响机理。另外, 草地土壤氮矿化以硝化作用为主, NO3--N是形成生物量的有效氮素。养分添加情景下, 土壤湿度是影响该区域温带草原土壤净氮矿化和硝化速率的主效因素。土壤微生物碳氮量并不能解释养分添加情景下的土壤氮矿化的变化。但非生物因子(如有机碳含量、土壤全氮及土壤C/N)能够较好地解释不同氮处理下温带草原净矿化及硝化速率的变化, 这些环境因子的变化在调控草地生态系统功能中具有重要的作用。此研究成果有助于更为准确地评估未来养分水平变化情境对温带草原生态系统服务功能和氮生物地球化学循环过程的影响。
致谢 感谢内蒙古大学毛登生态实验站给予本研究野外工作上的支持。
The authors have declared that no competing interests exist.
作者声明没有竞争性利益冲突.
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Chronic nitrogen additions at the Harvard Forest (USA): The first 15 years of a nitrogen saturation experiment. https://doi.org/10.1016/j.foreco.2004.03.009 URL [本文引用: 1] 摘要
The delivery of reactive forms of nitrogen to the environment through the sum of agricultural and industrial activities now exceeds that from natural processes. Potential negative effects on forests were first proposed in 1985, and in the ensuing two decades, the process of N saturation has become a well-established and generally understood phenomenon, with a few remaining, significant unknowns.One goal of this special section in Forest Ecology and Management is to report in detail on results from the first 15 years of chronic nitrogen additions to two contrasting forest types at the Harvard Forest in Petersham, MA, USA, with special reference to these two central questions. As similar projects elsewhere come to an end, the Harvard Forest experiment remains as one of the few on-going, long-term N saturation experiments. Longevity has enhanced the value of the chronic N experiment, and lead to a series of collaborative studies on plant, soil and microbial responses. Another goal of this special issue is to bring together and present the findings resulting from a diverse set of measurements enabled by the presence of this long-term experiment. A total of 11 papers are presented, in addition to this brief introduction.
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Carbon and nitrogen mineralization dynamics in different soils of the tropics amended with legume residues and contrasting soil moisture contents. https://doi.org/10.1007/s00374-011-0607-8 URL [本文引用: 1] 摘要
Seasonal drought in tropical agroecosystems may affect C and N mineralization of organic residues. To understand this effect, C and N mineralization dynamics in three tropical soils (Af, An 1 , and An 2 ) amended with haricot bean (HB; Phaseolus vulgaris L.) and pigeon pea (PP; Cajanus cajan L.) residues (each at 502mg02g 611 dry soil) at two contrasting soil moisture contents (pF2.5 and pF3.9) were investigated under laboratory incubation for 100–13502days. The legume residues markedly enhanced the net cumulative CO 2 –C flux and its rate throughout the incubation period. The cumulative CO 2 –C fluxes and their rates were lower at pF3.9 than at pF2.5 with control soils and also relatively lower with HB-treated than PP-treated soil samples. After 10002days of incubation, 32–42% of the amended C of residues was recovered as CO 2 –C. In one of the three soils (An 1 ), the results revealed that the decomposition of the recalcitrant fraction was more inhibited by drought stress than easily degradable fraction, suggesting further studies of moisture stress and litter quality interactions. Significantly ( p 65<650.05) greater NH 4 + –N and NO 3 61 –N were produced with PP-treated (C/N ratio, 20.4) than HB-treated (C/N ratio, 40.6) soil samples. Greater net N mineralization or lower immobilization was displayed at pF2.5 than at pF3.9 with all soil samples. Strikingly, N was immobilized equivocally in both NH 4 + –N and NO 3 61 –N forms, challenging the paradigm that ammonium is the preferred N source for microorganisms. The results strongly exhibited altered C/N stoichiometry due to drought stress substantially affecting the active microbial functional groups, fungi being dominant over bacteria. Interestingly, the results showed that legume residues can be potential fertilizer sources for nutrient-depleted tropical soils. In addition, application of plant residue can help to counter the N loss caused by leaching. It can also synchronize crop N uptake and N release from soil by utilizing microbes as an ephemeral nutrient pool during the early crop growth period.
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Fertilizer and previous land use effects on C and N mineralization in soils from Eucalyptus globulus plantations. |
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Effects of nitrogen deposition on soil nitrogen mineralization of Betula platyphylla forest in Daxing’an Mountains. Journal of Northeast Forestry University, 43(7), 78‒83. (in Chinese with English abstract)施氮量对大兴安岭白桦次生林土壤氮矿化的影响 .
以大兴安岭白桦天然次生林为研究对象，分析施氮量对土壤氮矿化的 影响。结果表明，白桦次生林土壤中铵态氮、硝态氮和有效氮质量分数在生长季间存在显著差异。总体上，土壤中有效氮素质量分数在7月份最高，5月份最低。白 桦次生林土壤中铵态氮、硝态氮和有效氮质量分数均随着氮沉降量的增加而增加；同时氮沉降也显著增加了土壤氨化速率、硝化速率和氮矿化速率，其中氨化速率的 增幅大于硝化速率的增幅。不同施氮处理下，净矿化速率与土壤有机碳质量分数间的相关性比与全氮质量分数间更为密切。
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Gross nitrogen mineralization-, immobilization-, and nitrification rates as a function of soil C/N ratio and microbial activity. https://doi.org/10.1016/S0038-0717(02)00248-1 URL [本文引用: 1] 摘要
A laboratory experiment was designed to challenge the idea that the C/N ratio of forest soils may control gross N immobilization, mineralization, and nitrification rates. Soils were collected from three deciduous forests sites varying in C/N ratio between 15 and 27. They were air-dried and rewetted to induce a burst of microbial activity. The N transformation rates were calculated from an isotope dilution and enrichment procedure, in which 15 NH 4 Cl or Na 15 NO 3 was repeatedly added to the soils during 7 days of incubation. The experiments suggested that differences in gross nitrogen immobilization and mineralization rates between the soils were more related to the respiration rate and ATP content than to the C/N ratio. Peaks of respiration and ATP content were followed by high rates of mineralization and immobilization, with 1鈥2 days of delay. The gross immobilization of NH 4 + was dependent on the gross mineralization and one to two orders of magnitude larger than the gross NO 3 鈭 immobilization. The gross nitrification rates were negatively related to the ATP content and the C/N ratio and greatly exceeding the net nitrification rates. Taken together, the observations suggest that leaching of nitrate from forest soils may be largely dependent on the density and activity of the microbial community.
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Organic matter accumulation and nitrogen mineralization during secondary succession in heathland ecosystems. https://doi.org/10.2307/2261121 URL [本文引用: 1] 摘要
Five series of plots in heathlands were selected in which the aboveground biomass and the litter (L) and humus (FH) layer had been removed 1-50 years beforehand. Secondary succession in these heathlands was studied by comparing the amounts of soil OM, aboveground biomass, belowground biomass and the annual N mineralization in plots of different ages. The amounts of OM in the L and FH layers inc...
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Comparison of methodologies for field measurement of net nitrogen mineralization in arable soils. |
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Grazing intensity alters soil respiration in an alpine meadow on the Tibetan Plateau. https://doi.org/10.1016/j.soilbio.2003.09.010 URL [本文引用: 1] 摘要
Grazing intensity may alter the soil respiration rate in grassland ecosystems. The objectives of our study were to (1) determine the influence of grazing intensity on temporal variations in soil respiration of an alpine meadow on the northeastern Tibetan Plateau; and (2) characterise, the temperature response of soil respiration under different grazing intensities. Diurnal and seasonal soil respiration rates were measured for two alpine meadow sites with different grazing intensities. The light grazing (LG) meadow site had a grazing intensity of 2.55 sheep ha(-1), while the grazing intensity of the heavy grazing (HG) meadow site, 5.35 sheep ha(-1), was approximately twice that of the LG site. Soil respiration measurements - showed that CO2 efflux was almost twice as great at the LG site as at the HG site during the growing season, but the diurnal and seasonal patterns of soil respiration rate were similar for the two sites. Both exhibited the highest annual soil respiration rate in mid-August and the lowest in January. Soil respiration rate was highly dependent on soil temperature. The Q(10) value for annual soil respiration was lower for the HG site (2.75) than for the LG site (3.22). Estimates of net ecosystem CO2 exchange from monthly measurements of biomass and soil respiration revealed that during the period from May 1998 to April 1999, the LG site released 2040 g CO2 m(-2) y(-1) to the atmosphere, which was about one third more than the 1530g CO2 m(-2) y(-1) released at the HG site. The results suggest that (1) grazing intensity alters not only soil respiration rate, but also the temperature dependence of soil CO2 efflux; and (2) soil temperature is the major environmental factor controlling the temporal variation of soil respiration rate in the alpine meadow ecosystem. (C) 2003 Elsevier Ltd. All fights reserved.
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Principles of Ter- restrial Ecosystem Ecology. Springer-Verlag , |
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Evaluation of different soil carbon determination methods. https://doi.org/10.1080/07352680902776556 URL [本文引用: 1] 摘要
Determining soil carbon (C) with high precision is an essential requisite for the success of the terrestrial C sequestration program. The informed choice of management practices for different terrestrial ecosystems rests upon accurately measuring the potential for C sequestration. Numerous methods are available for assessing soil C. Chemical analysis of field-collected samples using a dry combustion method is regarded as the standard method. However, conventional sampling of soil and their subsequent chemical analysis is expensive and time consuming. Furthermore, these methods are not sufficiently sensitive to identify small changes over time in response to alterations in management practices or changes in land use. Presently, several different in situ analytic methods are being developed purportedly offering increased accuracy, precision and cost-effectiveness over traditional ex situ methods. We consider that, at this stage, a comparative discussion of different soil C determination methods will improve the understanding needed to develop a standard protocol.
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Tem- perature responses of net nitrogen mineralization and nitrification in conifer forest soils incubated under standard laboratory conditions. |
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Relations between net nitrogen mineralization and soil characteristics within an arable field. https://doi.org/10.1080/090647102321089819 URL 摘要
Within-field variations in plant-available soil nitrogen (N) are likely to be affected by differences in soil characteristics. To study this, a 3- year field investigation was conducted during 1998-2000 on a 15 ha arable field in Sweden with considerable within-field soil texture variability. In 34 plots soil N uptake by crops, net nitrogen mineralization (Nm) during the growing season and soil mineral N in spring and shortly after harvest were determined. Beside these parameters, topography, soil organic matter content (SOM), clay content, pH(HO) and grain yield were recorded. The variations in Nm were considerably large both within the field and between years. The within-field variation in Nm could partly be explained by the variation in SOM and clay content (adjusted coefficient of determination = 0.23, <0.001). The pattern in Nm differed between years, partly because of seasonal variations in soil moisture. For these reasons, the pattern of Nm is difficult to predict without seasonal adjustments.
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| [13] |
Manipulation of fertiliser regimes in phosphorus enriched soils can reduce phosphorus loss to leachate through an increase in pasture and microbial biomass production. https://doi.org/10.1016/j.agee.2013.12.018 URL [本文引用: 1] 摘要
Phytoextraction of phosphorus (P) has been proposed as a strategy to reduce the potential for P loss from P enriched soils. Compared to pastures that receive adequate P fertilisers to maintain soil P concentrations, applying half maintenance rates, or no P, slowly decreases soil P concentration and P losses to water. We hypothesise that the quantity of P lost in leachate can be further decreased by the addition of nitrogen (N) fertiliser to stimulate plant-P uptake. A 451 day lysimeter trial investigated subsurface P losses from three New Zealand soil types (USDA soil taxonomy: Udand, Dystrudept and Vitrand) under three N fertiliser rates, zero, 150 and 300kgNha 611 yr 611 and two rates of P fertiliser, zero and half maintenance application with regular cutting and removal of pasture. For two of the soil types (Dystrudept and Vitrand), N application increased pasture production and decreased the load of dissolved reactive P (DRP) leached by 53–76% and the load of total dissolved P (TDP) by 39–53% compared to when no N was applied. Furthermore, for these soils, compared to the no P and no N treatment, applying P at half the rate designed to maintain soil P concentration, decreased the load of DRP and TDP in leachate by a 62–68% and 54–59% due to immobilisation of P within the microbial biomass. A high sorption capacity, leading to slow but sustained release of P to the soil solution, was seen as the probable reason for the lack of treatment effect in the third soil (Udand). This study highlights the potential for manipulating fertiliser regimes and implementing a cut and carry system on critical source areas of P loss within a farm as a strategy to reduce P loss from P enriched pastoral soils without impacting on productivity.
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| [14] |
Variation characteristics of soil respiration fluxes in four types of grassland communities under different precipitation intensity. Chinese Science Bulletin, 50, 583‒591. (in Chinese)不同降水强度4种草地群落土壤呼吸通量变化特征 .https://doi.org/10.3321/j.issn:0023-074X.2005.05.013 URL [本文引用: 1] 摘要
利用静态暗箱法,对内蒙古锡林河流域沿降水梯度4种半干旱草地类型进行了连续2年的野外定位试验,对比研究了沿降水梯度4种不同草地类型土壤呼吸通量的变化特征,统计分析了水热因子对草地土壤呼吸通量特征的可能影响,并建立了土壤呼吸通量与水热因子间的数值关系模式,同时利用野外连续完整的观测数据对不同草地类型土壤CO2年排放量分别进行了估算.结果表明土壤呼吸通量存在明显的季节变化规律,沿降水梯度各草地类型土壤呼吸通量的季节变化型式基本相同,各草地群落土壤呼吸均以春末和夏季较高,秋冬季排放量较低,不同草地类型冬季均观测到土壤呼吸的负通量,对其机制的进一步研究有利于对土壤年呼吸总量的准确估算;沿降水梯度4种草地类型土壤年(或生长季)呼吸量均沿降水梯度递减,表现为贝加尔针茅草原>羊草草原>大针茅草原>克氏针茅草原;不同草地类型土壤呼吸通量在植物生长季与0~10cm以及10~20cm土壤含水量均呈不同程度的正相关,而与气温和表层土壤温度的相关性较弱,4种草地类型生长季内土壤表层含水量的变化通常能解释土壤呼吸通量变异的70.2%~94.7%,而在植物非生长季,土壤呼吸通量更多地受气温及土壤表层地温的限制,温度条件的变化能解释土壤呼吸通量变化的70%以上.
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| [15] |
Global analysis of nitrogen and phosphorus limitation of primary producers in freshwater, marine and terrestrial ecosystems. https://doi.org/10.1111/j.1461-0248.2007.01113.x URL PMID: 17922835 [本文引用: 1] 摘要
The cycles of the key nutrient elements nitrogen (N) and phosphorus (P) have been massively altered by anthropogenic activities. Thus, it is essential to understand how photosynthetic production across diverse ecosystems is, or is not, limited by N and P. Via a large-scale meta-analysis of experimental enrichments, we show that P limitation is equally strong across these major habitats and that N and P limitation are equivalent within both terrestrial and freshwater systems. Furthermore, simultaneous N and P enrichment produces strongly positive synergistic responses in all three environments. Thus, contrary to some prevailing paradigms, freshwater, marine and terrestrial ecosystems are surprisingly similar in terms of N and P limitation.
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| [16] |
Predicting the effects of atmospheric nitrogen deposition in conifer stands: Evidence from NITREX ecosystem- scale experiments . |
| [17] |
Microbial biomass and nitrogen cycling responses to fertilization and litter removal in young northern hardwood forests. https://doi.org/10.1023/A:1010693614196 URL Magsci [本文引用: 1] 摘要
<a name="Abs1"></a>The influence of site fertility on soil microbial biomass and activity is not well understood but is likely to be complex because of interactions with plant responses to nutrient availability. We examined the effects of long-term (8 yr) fertilization and litter removal on forest floor microbial biomass and N and C transformations to test the hypothesis that higher soil resource availability stimulates microbial activity. Microbial biomass and respiration decreased by 20–30 % in response to fertilization. Microbial C averaged 3.8 mg C/g soil in fertilized, 5.8 mg C/g in control, and 5.5 mg C/g in litter removal plots. Microbial respiration was 200 µg CO<sub>2</sub>-C g<sup>–1</sup> d<sup>–1</sup> in fertilized plots, compared to 270 µg CO<sub>2</sub>-C g<sup>–1</sup> d<sup>–1</sup> in controls. Gross N mineralization and N immobilization did not differ among treatments, despite higher litter nutrient concentrations in fertilized plots and the removal of substantial quantities of C and N in litter removal plots. Net N mineralization was significantly reduced by fertilization. Gross nitrification and NO<sub>3</sub><sup>–</sup> immobilization both were increased by fertilization. Nitrate thus became a more important part of microbial N cycling in fertilized plots even though NH<sub>4</sub><sup>+</sup> availability was not stimulated by fertilization.<div class="AbstractPara"><div class="">Soil microorganisms did not mineralize more C or N in response to fertilization and higher litter quality; instead, results suggest a difference in the physiological status of microbial biomass in fertilized plots that influenced N transformations. Respiration quotients (qCO<sub>2</sub>, respiration per unit biomass) were higher in fertilized plots (56 µg CO<sub>2</sub>-C mg C<sup>–1</sup> d<sup>–1</sup>) than control (48 µg CO<sub>2</sub>-C mg C<sup>–1</sup> d <sup>–1</sup>) or litter removal (45 µg CO<sub>2</sub>-C mg C<sup>–1</sup> d<sup>–1</sup>), corresponding to higher microbial growth efficiency, higher proportions of gross mineralization immobilized, and lower net N mineralization in fertilized plots. While microbial biomass is an important labile nutrient pool, patterns of microbial growth and turnover were distinct from this pool and were more important to microbial function in nitrogen cycling.
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| [18] |
Temporal and spatial patterns of soil nitrogen mineralization and nitrification in four temperate forests. Acta Ecologica Sinica, 29, 3747‒ 3758. (in Chinese with English abstract)四种温带森林土壤氮矿化与硝化时空格局 .https://doi.org/10.3321/j.issn:1000-0933.2009.07.036 URL [本文引用: 1] 摘要
利用PVC管原位培养连续取样 法测定了东北地区4种具有代表性的森林生态系统(硬阔叶林、蒙古栎林、红松林、落叶松林)土壤氮素矿化、硝化的时间动态及氮矿化的空间分布格局。结果表 明:4种森林土壤氮素矿化存在明显的时空变异。蒙古栎和红松林土壤在6月份表现出强烈的氮矿化和硝化作用,而硬阔叶林及落叶松林7月份氮素矿化强烈。4种 森林生态系统上层土壤的氮净矿(硝)化率显著高于下层土壤。4种林型土壤的硝化过程在氮矿化过程中占有重要地位,其NO3--N在无机氮中的比例分别 为:79.9%～91.1%(硬阔叶林)、50.7%～80.5%(蒙古栎林)、54.1%～92.0%(红松林)、63.7%～86.5%(落叶松 林)。生态系统构成决定了土壤氮素的矿化能力。阔叶林和针阔混交林生态系统矿化率大于纯针叶林生态系统。硬阔叶林、红松林、蒙古栎林、落叶松林的平均净矿 化率分别为:(0.58±0.01)mg.kg-1.d-1、(0.47±0.19)mg.kg-.1d-1、 (0.39±0.11)mg.kg-.1d-1和(0.23±0.06)mg.kg-.1d-1。4种林型氮素矿化作用与地下5cm温度呈正相关,并受土 壤表层(0～10cm)水分显著影响。土壤微生物量氮与土壤氮矿化呈显著正相关。
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| [19] |
Impact of nitrogen deposition on nitrogen cycling in forests: A synthesis of NITREX data. https://doi.org/10.1016/S0378-1127(97)00124-2 URL 摘要
Impact of nitrogen (N) deposition was studied by comparing N fluxes, N concentrations and N pool sizes in vegetation and soil in five coniferous forest stands at the NITREX sites: G02rdsj02n (GD), Sweden, Klosterhede (KH), Denmark, Aber (AB), Wales, UK, Speuld (SP), the Netherlands, and Ysselsteyn (YS), the Netherlands. The sites span a N- deposition gradient from 13 to 59 kg N ha 611 yr 611 . Measurements of soil N transformation rates by laboratory and field incubations were part of the site comparison. Further, results from 4–5 yr of NH 4 NO 3 addition (35 kg N ha 611 yr 611 ) at low deposition sites (GD, KH, AB) and 6 yr of N removal (roofs) at high deposition sites (SP, YS) were included in the analysis. Significant correlations were found between a range of variables including N concentrations in foliage and litter, soil N transformation rates and forest floor characteristics. Using the methods from principal component analysis (PCA) these variables were summarized to an index of site N status that assigned the lowest N status to GD and the highest to YS. Site N status increased with N deposition with the exception that AB was naturally rich in N. Nitrate leaching was significantly correlated with N status but not correlated with N deposition. Forest floor mass and root biomass decreased with increased N status. Characteristics of the mineral soil were not correlated with vegetation and forest floor variables. High ja:math ratios in the mineral soil at the high-N deposition sites (SP, YS) suggest that the mineral soil pool changes slowly and need not change for N saturation to occur. Nitrogen transformation rates measured in laboratory incubations did not agree well with rates measured in the field except for a good correlation between ‘gross’ mineralization in the laboratory and ‘net’ mineralization in the field. The changes in N concentrations and fluxes after manipulation of N input followed the direction expected from the site comparison: increases at N addition and decreases at N removal sites. Nitrate leaching responded within the first year of treatment at all sites, whereas responses in vegetation and soil were delayed. Changes in N status by the manipulation treatments were small compared to the differences between sites. Changes in nitrate leaching were small at the low-N status sites and substantial at the high-N status sites. Nitrogen-limited and N-saturated forest ecosystems could be characterized quantitatively.
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| [20] |
Nitrogen mineralization in marsh meadows in relation to soil organic matter content and watertable level. https://doi.org/10.1002/1522-2624(200110)164:53.0.CO;2-P URL [本文引用: 1] 摘要
Abstract The objective of the present study was to asses the effect of watertable level on N mineralization in a Histosol and a Humic Gleysol profile under natural meadows in Ljubljana marsh, Slovenia. The two soils differ significantly in organic matter content (27—4061% in Histosol and 14—2061% in Humic Gleysol) but not in C61:61N ratio (13—20) and pH (6.5—7.0). For each soil, the watertable was maintained at two levels (above or below 50 cm from the soil surface) for approximately one year. The four main plots, according to soil carbon content and watertable level were divided into 4 subplots, according to 4 fertilization treatments (unfertilized control, PK, PK + 50 kg N ha —1 , PK + 3 × 50 kg N ha —1 ). Net N mineralization in unfertilized subplots was estimated from indices of N mineralization obtained by incubation of soil samples in the laboratory and by seasonal dynamics of mineral N content in the field. Annual uptake of N in herbage under the 4 fertilization treatments was also measured. Total mineral N content in topsoil was 20—8061% higher in Histosol than in Humic Gleysol. Similarly, aerobic N mineralization potentials along the entire soil profile (0—90 cm) were 20—13061% higher in Histosol than in Humic Gleysol. By contrast, anaerobic N mineralization potentials in subsoil were 10—6061% lower in Histosol than in Humic Gleysol. Both, aerobic and anaerobic N mineralization potentials strongly depended on watertable levels at sampling time. Seasonal dynamics of soil mineral N content as well as N mineralization potentials indicated that the N mineralization in the Histosol could be 10—4061% higher at low than at high watertable level. In the Humic Gleysol the N mineralization could be 10—10061% higher at high watertable level. Higher N availability in Histosol at low watertable and in Humic Gleysol at high watertable was also reflected in higher N uptake in herbage. These results indicate that N mineralization in Histosol and Humic Gleysol, was proportional to soil organic matter content, whereas in both soils, higher N mineralization rates can be expected at watertable levels between 40 and 60 cm below the soil surface, than at higher/lower watertable levels. Einfluss des Humusgehaltes und des Grundwasserspiegels auf die Stickstoffmineralisation in B02den aus Feuchtgebieten Ziel dieser Untersuchung war es, den Einfluss der H02he des Grundwasserspiegels auf die N-Mineralisation in einem Histosol und einem Humic Gleysol unter Naturwiesen des Ljubljanaer Moors, Slowenien, festzustellen. Die zwei untersuchten Bodentypen unterscheiden sich signifikant im Gehalt der organischen Substanzen (27—4061% in Histosol und 14—2061% in Humic Gleysol), aber nicht im C61:61N-Verh01ltnis und pH-Wert (6.5—7.0). In jedem Bodentyp wurden für die Dauer von 1 Jahr künstlich jeweils ein hoher und ein niedriger Grundwasserspiegel eingestellt. Jede der 4 daraus resultierenden Haupt-Versuchsparzellen wurde weiter geteilt in 4 Düngungs-Teilstücke: Ungedüngt, PK, PK + 50 kg N ha —1 und PK + 3 × 50 kg N ha —1 . Die Netto-N-Mineralisation auf ungedüngten Teilstücken der Haupt-Versuchparzellen (2 Bodentypen, 2 Grundwasserspiegel) wurde bestimmt durch die N-Mineralisationspotenziale bei anaerober und aerober Inkubation der Bodenproben im Labor sowie durch die saisonale Dynamik des N-Gehaltes im Boden sowie durch den N-Entzug der Vegetation in 4 Düngungsvarianten. W01hrend der Messperiode lag der Gehalt am gesamten mineralischen Stickstoff in der oberen Bodenschicht des Histosol um 20 bis 8061% h02her als im Humic Gleysol. 02hnlich waren die aeroben N-Mineralisationspotenziale im Bodenprofil des Histosols um 20 bis 13061% h02her als im Humic Gleysol. Die anaeroben N-Mineralisationspotenziale waren dagegen in tieferen Bodenschichten des Histosol um 10 bis 6061% niedriger als im Humic Gleysol. Die 02nderungen der Mineralisationspotenziale in aerob und anaerob inkubierten Bodenproben waren zugleich vom Grundwasserspiegel zur Zeit der Beprobung abh01ngig. Sowohl die zeitliche Dynamik des Gehaltes an mineralischem N in der Zeit als auch die aeroben und anaeroben N-Mineralisationspotenziale zeigen aber einheitlich, dass die N-Mineralisation im Histosol bei niedrigem Grundwasserspiegel um 10 bis 4061% gr0208er sein kann, w01hrend im Humic Gleysol die N-Mineralisation bei hohem Grundwasserspiegel um 10 bis 10061% gr0208er sein kann. H02here N-Verfügbarkeit im Boden widerspiegelt sich auch im h02heren N-Entzug durch die Vegetation. Die Ergebnisse dieser relativ kurzen Untersuchung zeigen, dass die N-Mineralisation in Histosol und in Humic Gleysol proportional dem Humusgehalt verl01uft; in beiden Bodentypen kann bei Grundwasserspiegeln von 40—60 cm eine st01rkere N-Mineralisation erwartet werden als bei darüber oder darunter liegendem Wasserspiegel.
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| [21] |
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| [22] |
Relationship between habit able pore space, soil biota and mineralization rates in grassland soils. |
| [23] |
Soil microbial biomass dynamic sonnet nitrogen mineralization in northern hardwood ecosystem. |
| [24] |
Microbial N turnover and N-oxide (N2O/NO/NO2) fluxes in semi-arid grassland of Inner Mongolia. |
| [25] |
Effects of nitrogen addition on nitrogen mineralization and nutrient content of expanding Calamagrostis epigejos in the Podyjí National Park, Czech Republic.
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| [26] |
Nitrogen limitation in dryland ecosystems: Responses to geographical and temporal variation in precipitation. https://doi.org/10.1007/BF01007582 URL [本文引用: 1] 摘要
We investigated the relationship between plant nitrogen limitation and water availability in dryland ecosystems. We tested the hypothesis that at lower levels of annual precipitation, aboveground net primary productivity (ANPP) is limited primarily by water whereas at higher levels of precipitation, it is limited primarily by nitrogen. Using a literature survey of fertilization experiments in arid, semi-arid, and subhumid ecosystems, we investigated the response of ANPP to nitrogen addition as a function of variation in precipitation across geographic gradients, as well as across year-to-year variation in precipitation within sites. We used four different indices to assess the degree of N limitation: (1) Absolute Increase of plant production in response to fertilization (the slope of ANPP vs. amount of added N at different levels of annual precipitation); (2) Relative Response (the percent increase in fertilized over control ANPP at different levels of N addition); (3) Fertilizer Use Efficiency (FUE, the absolute gain in productivity per amount of fertilizer N), and (4) Maximum Response (the greatest absolute increase in ANPP at saturating levels of N addition). Relative Response to fertilization did not significantly increase with increasing precipitation either across the geographic gradient or across year-to-year variation within sites. Nor did the Maximum Response to fertilization increase with increasing precipitation across the geographic gradient. On the other hand, there was a significant increase in the Absolute Increase and FUE indices with both geographical and temporal variation in precipitation. Together, these results indicate that there is not necessarily a shift of primary limitation from water to N across the geographic water availability gradient. Instead, our results support the hypothesis of co-limitation. The apparently contradictory results from the four indices of N limitation can best be explained by an integration of plant ecophysiological, community, and ecosystem mechanisms whereby plants are co-limited by multiple resources, species shifts occur in response to changing resource levels, and nitrogen and water availability are tightly linked through biogeochemical feedbacks.
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| [27] |
Effect of fertilize application and fire regime on soil mineralization in an Australia sub alpine eucalypt forest. |
| [28] |
N deposition, N transformation and N leaching in acid forest soils. https://doi.org/10.1023/B:BIOG.0000031050.13663.82 URL [本文引用: 1] 摘要
Nitrogen deposition, mineralisation, uptake and leaching were measured on a monthly basis in the field during 2 years in six forested stands on acidic soils under mountainous climate. Studies were conducted in three Douglas-fir [(Mirb.) Franco] plantations (D20: 20 year; D40: 40 yr; D60: 60 yr) on abandoned croplands in the Beaujolais Mounts; and two spruce (Karst.) plantations (S45: 45 yr; S90: 90 yr) and an old beech (L.) stand (B150: 150 yr) on ancient forest soils in a small catchment in the Vosges Mountains. N deposition in throughfall varied between 7–8 kg hayear(D20, B150, S45) and 15–21 kg hayr(S90, D40, D60). N in annual litterfall varied between 20–29 kg ha(D40, D60, S90), and 36–43 kg ha(D20, S45, B150). N leaching below root depth varied among stands within a much larger range, between 1–9 kg hayr(B150, S45, D60) and 28–66 kg hayr(D40, S90, D20), with no simple relationship with N deposition, or N deposition minus N storage in stand biomass. N mineralisation was between 57–121 kg hayr(S45, D40, S90) and between 176–209 kg hayrin (B150, D60 and D20). The amounts of nitrogen annually mineralised and nitrified were positively related. Neither general soil parameters, such as pH, soil type, base saturation and C:N ratio, nor deposition in throughfall or litterfall were simply related to the intensity of mineralisation and/or nitrification. When root uptake was not allowed, nitrate leaching increased by 11 kg hayrat S45, 36 kg hayrat S90 and between 69 and 91 kg hayrat D20, D40, B150 and D60, in relation to the nitrification rates of each plot. From this data set and recent data from the literature, we suggest that: high nitrification and nitrate leaching in Douglas-fir soils was likely related to the former agricultural land use. High nitrification rate but very low nitrate leaching in the old beech soil was related to intense recycling of mineralised N by beech roots. Medium nitrification and nitrate leaching in the old spruce stand was related to the average level of N deposition and to the deposition and declining health of the stand. Very low nitrification and N leaching in the young spruce stand were considered representative of fast growing spruce plantations receiving low N deposition on acidic soils of ancient coniferous forests. Consequently, we suggest that past land use and fine root cycling (which is dependent on to tree species and health) should be taken into account to explain the variability in the relation between N deposition and leaching in forests.
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| [29] |
Factors controlling mineralization of soil organic matter in the Eurasian steppe. https://doi.org/10.1016/j.soilbio.2007.11.015 URL [本文引用: 1] 摘要
To understand the dynamics of soil organic matter (SOM) in the Eurasian steppe, several soil and meteorological properties were tested in order to estimate the amounts of potentially mineralizable organic carbon (PMC) and nitrogen (PMN). Total 41 surface soil samples were collected in Ukraine and Kazakhstan from cropland, forest, grassland, and desert ecosystems. The fresh soils were incubated for 133 days under constant temperature and moisture conditions, and the CO 2 emissions and the mineral N from the soils were monitored. PMC and PMN were determined by fitting models to the cumulative curves of the CO 2 and the mineral N. Tested soil properties included soil pH, sand, silt and clay contents, carbon and nitrogen contents of light fraction (LF, <1.6聽g聽cm 鈭3 ) and heavy fraction (HF), and C/N ratio of LF and HF. The meteorological properties considered were mean annual temperature and precipitation. Using multiple regression analysis with the stepwise method, PMC was well estimated by carbon content of LF (LFC) and clay content, compared to the simple correlation with organic carbon (OC). Similarly, PMN was better determined by nitrogen content of LF (LFN) and clay content. These results suggest the partially labile nature of clay-associating OM and of LFC and LFN. The higher PMC and PMN in the forest and grassland sites would be attributed to the higher LFC and LFN, while the lower LFC and LFN in cropland sites would suggest the relatively higher contribution of clay-associating OM to PMC and PMN.
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| [30] |
Soil nitrogen dynamics along a gradient of long-term soil development in a Hawaiian wet montane rain forest. |
| [31] |
Nitrogen deposition and forest expansion in the northern Great Plains. https://doi.org/10.1046/j.0022-0477.2001.00600.x URL [本文引用: 1] 摘要
Summary Top of page Summary Introduction Methods Results Discussion Acknowledgements References 1 Atmospheric nitrogen (N) deposition has become one of the most important agents of vegetation change in densely populated regions. It may also contribute to forest expansion into grasslands at the northern edge of the North American Great Plains. 2 We measured N deposition and available soil N with ion-exchange resin over 2 years in six national parks in areas varying in population density and industrialization. N deposition was significantly higher in four parks in densely populated regions than in two remote parks. 3 Available soil N increased significantly with N deposition across all parks. 4 We measured N mass and 15 N abundance (δ 15 N) in vegetation and soil in two parks: Elk Island, receiving 22kgNha 611 year 611 , and Jasper, receiving 8kgNha 611 year 611 . Differences between parks in tissue N concentrations were small, but forest expansion over five decades resulted in the mass of N in vegetation increasing by 74% in Elk Island but by only 26% in Jasper. δ 15 N in forest vegetation was significantly lower in Elk Island than in Jasper, suggesting that anthropogenic sources contribute significantly to the high rates of N entering that ecosystem. 5 We determined the rate of forest expansion within parks using six decades of aerial photographs. Parks in aspen parkland and boreal forest showed a strong positive relationship between forest expansion and N deposition. The relationships found between N deposition, available soil N and forest expansion suggest that even comparatively low rates of N deposition may accelerate the expansion of forest into temperate grasslands.
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| [32] |
Soil microbial properties under N and P additions in a semi-arid, sandy grassland. https://doi.org/10.1007/s00374-010-0463-y URL Magsci [本文引用: 2] 摘要
Surface (0–15 cm) soil samples were collected from a semi-arid, sandy grassland in Keerqin Sandy Lands, Northeast China to study changes in soil microbial and chemical properties after five consecutive years of nitrogen (N) and phosphorus (P) additions. Nitrogen and P additions and their interactions negligibly affected soil organic carbon and total N contents, while P addition significantly increased soil total P content. Soil pH was significantly decreased by N addition, which significantly increased net nitrification rate, whereas it did not affect net N mineralization rate. No significant effects of N and P additions and their interactions on basal respiration were detected. In addition, N addition significantly decreased microbial biomass C (MBC) and N, and thus microbial quotient, but increased dissolved organic C and microbial metabolic quotient due to the significant decrease of MBC. Our results suggest that in the mid-term the addition of N, but not P, can change soil microbial properties, with a possible decline in soil quality of semi-arid, sandy grasslands.
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| [33] |
Decadal-scale dynamics of water, carbon and nitrogen in a California chaparral ecosystem: DAYCENT modeling results. https://doi.org/10.1007/s10533-005-1391-z URL Magsci [本文引用: 1] 摘要
<a name="Abs1"></a>The Mediterranean climate, with its characteristic of dry summers and wet winters, influences the hydrologic and microbial processes that control carbon (C) and nitrogen (N) biogeochemical processes in chaparral ecosystems. These biogeochemical processes in turn determine N cycling under chronic N deposition. In order to examine connections between climate and N dynamics, we quantified decadal-scale water, C and N states and fluxes at annual, monthly and daily time steps for a California chaparral ecosystem in the Sierra Nevada using the DAYCENT model. The daily output simulations of net mineralization, stream flow and stream nitrate (NO<sub>3</sub><sup>−</sup>) export were developed for DAYCENT in order to simulate the N dynamics most appropriate for the abrupt rewetting events characteristic of Mediterranean chaparral ecosystems. Overall, the magnitude of annual modeled net N mineralization, soil and plant biomass C and N, nitrate export and gaseous N emission agreed with those of observations. Gaseous N emission was a major N loss pathway in chaparral ecosystems, in which nitric oxide (NO) is the dominant species. The modeled C and N fluxes of net primary production (NPP), N uptake and N mineralization, NO<sub>3</sub><sup>−</sup> export and gaseous N emission showed both high inter-annual and intra-annual variability. Our simulations also showed dramatic fire effects on NPP, N uptake, N mineralization and gaseous N emission for three years of postfire. The decease in simulated soil organic C and N storages was not dramatic, but lasted a longer time. For the seasonal pattern, the predicted C and N fluxes were greatest during December to March, and lowest in the summer. The model predictions suggested that an increase in the N deposition rate would increase N losses through gaseous N emission and stream N export in the chaparral ecosystems of the Sierra Nevada due to changes in N saturation status. The model predictions could not capture stream NO<sub>3</sub><sup>−</sup> export during most rewetting events suggesting that a dry-rewetting mechanism representing the increase in N mineralization following soil wetting needs to be incorporated into biogeochemical models of semi-arid ecosystems.
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| [34] |
Effect of nitrogen addition and mowing on soil nitrogen minerali- zation in abandoned grasslands in Inner Mongolia. 氮素添加和刈割对内蒙古弃耕草地土壤氮矿化的影响 .https://doi.org/10.5846/stxb201403040364 URL Magsci [本文引用: 7] 摘要
以内蒙古多伦县恢复生态学试验示范研究站弃耕10余年的草地为研究对象,于2006年起分别设置对照、氮素添加、刈割和氮素添加+刈割4种处理,每种处理6次重复,研究弃耕草地氮素添加和刈割对土壤氮矿化的影响,结合土壤理化性质和植被地上生产力的动态变化,分析弃耕草地土壤氮矿化对植被恢复的响应,为当地草地恢复与重建提供理论依据和数据支持。实验结果表明:① 氮素添加显著增加了植物地上净初级生产力(ANPP)和土壤无机氮库,与对照相比分别提高115% 和196%,同时显著提高了土壤总硝化速率;但是氮素添加对总氨化速率、土壤微生物生物量碳(MBC)、微生物生物量氮(MBN)、微生物生物量碳氮比(MBC/MBN)、微生物呼吸(MR)以及呼吸熵(<i>q</i>CO<sub>2</sub>)均无显著影响;② 总氨化速率和硝化速率对刈割处理的响应均不显著,但是刈割处理显著降低了土壤MR(<i>P</i>< 0.05);③ 氮素添加+刈割处理5-7a后,土壤总氨化和硝化速率均无显著变化;但是氮素添加+刈割处理显著增加了ANPP、土壤无机氮库和<i>q</i>CO<sub>2</sub>,同时显著降低了MBC和MBC/MBN。这说明在弃耕草地适应性管理中,氮素添加可以显著提高草地生产力,但是长期的氮添加对土壤微生物氮的转化是否有利还值得我们进一步研究。
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| [35] |
Enhanced nitrogen deposition over China. https://doi.org/10.1038/nature11917 URL Magsci 摘要
China is experiencing intense air pollution caused in large part by anthropogenic emissions of reactive nitrogen(1,2). These emissions result in the deposition of atmospheric nitrogen (N) in terrestrial and aquatic ecosystems, with implications for human and ecosystem health, greenhouse gas balances and biological diversity(1,3-5). However, information on the magnitude and environmental impact of N deposition in China is limited. Here we use nationwide data sets on bulk N deposition, plant foliar N and crop N uptake (from long-term unfertilized soils) to evaluate N deposition dynamics and their effect on ecosystems across China between 1980 and 2010. We find that the average annual bulk deposition of N increased by approximately 8 kilograms of nitrogen per hectare (P < 0.001) between the 1980s (13.2 kilograms of nitrogen per hectare) and the 2000s (21.1 kilograms of nitrogen Per hectare). Nitrogen deposition rates in the industrialized and agriculturally intensified regions of China are as high as the peak levels of deposition in northwestern Europe in the 1980s(6), before the introduction of mitigation measures(7,8). Nitrogen from ammonium (NH4+) is the dominant form of N in bulk deposition, but the rate of increase is largest for deposition of N from nitrate (NO3-), in agreement with decreased ratios of NH3 to NOx emissions since 1980. We also find that the impact of N deposition on Chinese ecosystems includes significantly increased plant foliar N concentrations in natural and semi-natural (that is, non-agricultural) ecosystems and increased crop N uptake from long-term-unfertilized crop-lands. China and other economies are facing a continuing challenge to reduce emissions of reactive nitrogen, N deposition and their negative effects on human health and the environment.
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| [36] |
Drivers of soil net nitrogen mineralization in the temperate grasslands in In- ner Mongolia, China. |
| [37] |
Effects of simulated nitrogen deposition on soil net nitrogen mineralization in the meadow steppe of Inner Mongolia, China. https://doi.org/10.1371/journal.pone.0134039 URL 摘要
Effects of simulated nitrogen (N) deposition on soil net nitrogen mineralization (NNM) were examined in situ during two growing seasons, using the resin-core technique in the semiarid meadow steppe in Inner Mongolia, China. The aim of this study is to clarify the effect of N levels (0, 10, and 20 kg N ha 鈭1 yr 鈭1 ) and forms (NH 4 + and NO 3 - ) on soil mineral N and NNM. Our results showed that N levels had no significant differences on soil mineral N and NNM. In the first year, three N treatments ((NH 4 ) 2 SO 4 , NH 4 Cl and KNO 3 ) increased soil NH 4 + concentrations but had no significant effects on soil NO 3 - concentrations. In the second year, (NH 4 ) 2 SO 4 treatment increased soil NO 3 - concentrations, NH 4 Cl and KNO 3 treatments decreased them. Three N treatments significantly decreased soil NH 4 + concentrations in the later stages of the second year. As for the soil NNM, three N treatments had no significant effects on the rates of soil NNM ( R m ) and net nitrification ( R n ) in the first year, but significantly decreased them in the second year. The contribution of N addition to R m was higher from (NH 4 ) 2 SO 4 than from NH 4 Cl and KNO 3 . However, Soil R m was mainly affected by soil water content (SWC), accumulated temperature (T a ), and soil total N (TN). These results suggest that the short-term atmospheric N deposition may inhibit soil NNM in the meadow steppe of Inner Mongolia.
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| [38] |
Effects of elevated CO2 temperature and N fertilization on fluxes in a grassland ecosystem. |
| [39] |
Spatial and temporal patterns of nitrogen deposition in China: Synthesis of observational data. |
| [40] |
The effects of warming and nitrogen addition on soil nitrogen cycling in a temperate grassland, north- eastern China. |
| [41] |
Fate of microbial biomass-derived amino acids in soil and their contribution to soil organic matter. https://doi.org/10.1016/j.orggeochem.2009.06.008 URL Magsci [本文引用: 1] 摘要
<h2 class="secHeading" id="section_abstract">Abstract</h2><p id="">Soil organic matter (SOM) is important for soil fertility and for the global C cycle. Previous studies have shown that during SOM formation no new compound classes are formed and that it consists basically of plant- and microorganism-derived materials. However, little data on the contribution from microbial sources are available. Therefore, we investigated previously in a model study the fate of C from <sup>13</sup>C-labelled Gram-negative bacteria in soil (Kindler, R., Miltner, A. Richnow, H.H., Kästner, M., 2006. Fate of gram negative bacterial biomass in soil – mineralization and contribution to SOM. Soil Biology and Biochemistry 38, 2860–2870) and showed that 44% of the bulk <sup>13</sup>C remained in the soil. Here we present the corresponding data on the fate of amino acids hydrolysed from proteins, which are the most abundant components of microbial biomass. After 224 days incubation, the label in the total amino acids in the soil amended with <sup>13</sup>C-labelled cells decreased only to >95%. The total amino acids therefore clearly showed a lower turnover than the bulk <sup>13</sup>C and a surprisingly stable concentration. Proteins therefore have to be considered as being stabilised in soil in dead, non-extractable biomass or cell fragments by known general stabilisation mechanisms. The label in the amino acids in a fraction highly enriched in living microbial biomass decreased to a greater extent, i.e. to 25% of the initially added amount. The amino acids removed from this fraction were redistributed via the microbial food web to non-living SOM. All amino acids in the microbial biomass were degraded at similar rates without a change in isotopic signature. The nuclear magnetic resonance (NMR) spectra of the soils were very similar and indicate that the residues of the degraded microbial biomass were very similar to those of the SOM and are a significant source for the formation of the SOM.</p>
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| [42] |
Calcium and phosphorus interact to reduce mid-growing season net nitrogen mineralization potential in organic horizons in a northern hardwood forest. https://doi.org/10.1016/j.soilbio.2010.10.009 URL [本文引用: 1] 摘要
Acid deposition can deplete soil (Ca) and be detrimental to the health of some forests. We examined effects of soil Ca and (P) availability on microbial activity and (N) transformations in a plot-scale nutrient addition experiment at the Hubbard Brook Experimental Forest in New Hampshire, USA. We tested the hypotheses that (1) microbial activity and N transformations respond to large but not small changes in soil Ca, (2) soil Ca availability influences net N via the immobilization of N, rather than via changes in microbial activity, and (3) the response to Ca is constrained by P availability. Seasonality was a primary influence on the microbial response to treatments; N cycling processes varied from May to October and treatment effects were only detectable in the mid-growing season, in July. Neither microbial activity (C ) nor gross N responded to Ca or to P, in either horizon. In the Oa horizon in July net N was reduced by high Ca and by Ca + P, and gross nitrification was increased by P addition. In the Oe horizon in July net N was reduced by Ca + P. These results partially supported our hypotheses, suggesting that soil Ca depletion has the potential to increase mid-growing season N availability via subtle changes in N immobilization, and that this effect is sensitive to soil P chemistry. The horizon-specific nature of the responses that we detected suggests that the proportions of Oe and Oa horizons comprising the surface organic layer will influence the relative importance of these processes at the ecosystem scale. Our results highlight the need for further attention to seasonal changes in controls of microbial /immobilization processes, to functional differences between organic horizons, and to interactions between Ca and P in soils, in order to learn the specific mechanisms underlying the influence of Ca status on nutrient recycling in these northern hardwood ecosystems.
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| [43] |
Estimation of parameters in complex 15N tracing models by Monte Carlo sampling. |
| [44] |
|
| [45] |
The effect of a perennial cover crop on net soil N mineralization and microbial biomass carbon in coconut plantations in the humid tropics. |
| [46] |
Seasonal dynamics of mineral N pools and N-mineralization in soils under homegarden trees in South Andaman, India. https://doi.org/10.1007/s10457-007-9073-6 URL Magsci [本文引用: 1] 摘要
<a name="Abs1"></a>Agroforestry trees are now well known to play a central role in the build up of nutrients pools and their transformations similar to that of forest ecosystem, however, information on the potential of homegarden trees accumulating and releasing nitrogen (mineralization) is lacking. The present study reports seasonal variations in pool sizes of mineral N (NH<sub>4</sub><sup>+</sup>-N and NO<sub>3</sub><sup>−</sup>-N), and net N-mineralization rate in relation to rainfall and temperature under coconut (<i>Cocos nucifera</i> L.), clove (<i>Eugenia caryophyllata</i> Thunb) and nutmeg (<i>Myristica fragrans</i> Houtt. Nees) trees in a coconut-spice trees plantation for two annual cycles in the equatorial humid climate of South Andaman Island of India. Concentration of NH<sub>4</sub><sup>+</sup>-N was the highest during wet season (May–October) and the lowest during post-wet season (November–January) under all the tree species. On the contrary, concentration of NO<sub>3</sub><sup>−</sup>-N was the lowest in the wet season and the highest during the post-wet season. However, concentrations of the mineral N were the highest under the nutmeg and the lowest under the coconut trees. Like the pool sizes, mean annual mineralization was the highest under the nutmeg (561 mg kg<sup>−1</sup> yr<sup>−1</sup>) and the lowest under the coconut trees (393 mg kg<sup>−1</sup> yr<sup>−1</sup>). Rate of mineralization was the highest during the post-wet season and the lowest during the dry season (February–April) under all the tree species. High rainfall during the wet season, however, reduced the rate of nitrification under all the tree species. The mean annual mineralization was logarithmically related with rainfall amount and mean monthly temperature.
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| [47] |
Aboveground production and N and P cycling along a nitrogen mineralization gradient on Blackhawk Island, Wisconsin. https://doi.org/10.2307/1939478 URL [本文引用: 1] 摘要
ABSTRACT Net aboveground production (4.1-9.5 Mg.ha-1.yr-1) across a series of edaphic climax forests was highly correlated with field measurements of soil N mineralization (26-84 kg/ha-1yr-1) and with soil silt + clay content (5-74%). Soil N mineralization was positively correlated with litter production and N and P return in litter. Soil N mineralization was negatively correlated with litter C:N and C:P ratios and with efficiency of P use in litter production. Efficiency of N use in litter production declined with increasing N mineralization except for inefficient use of N in a hemlock stand at low N mineralization. Changes in litter quality across the mineralization-soil texture gradient were due to species replacement rather than changes in litter quality within each species. Nitrification was not correlated with aboveground production. Both mineralization and nitrification were highly correlated with humus P content. Differences in nitrification among the soils appeared to be related to PO4-P supply in the spring and early summer and to NH4-N supply in mid- to late summer.-Authors
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| [48] |
Spatial distribution of grassland biomass in China. 中国草原植被生物量及其空间分布格局 . |
| [49] |
Relationship between soil microbial biomass and gross N mineralization. |
| [50] |
Effects of precipitation change on inorganic nitrogen and net nitrogen mineralization rate at a planta- tion of mongolian pine. Acta Scientiarum Naturalium Universitatis Pekinensis, 48, 925‒932. (in Chinese with English abstract)降水变化对樟子松人工林土壤无机氮和净氮矿化速率的影响 .
在北京大学地球环境与生态系统塞罕坝实验站的樟子松(Pinus sylvestris var.mongolica)人工林内,采用野外降水控制实验和顶盖埋管法,在生长季内分0～5,5～10,10～20和20～30 cm 4层,研究穿透雨增加或减少30％对土壤无机氮(铵态氮与硝态氮之和)及净氮矿化速率的影响.结果表明,樟子松人工林地下0～30 cm无机氮含量为6.70±2.31 mg/kg,其中铵态氮5.59±1.78 mg/kg,硝态氮1.11±0.77mg/kg.不同土壤深度的无机氮含量无显著差异,3种穿透雨处理间的土壤铵态氮和无机氮含量无显著差异,增雨处理 的硝态氮含量显著低于对照.0～30 cm的土壤净氮矿化速率为-0.24 (-6.65～10.24) mg/(kg.30d).穿透雨处理和土壤深度对净氨化速率无显著影响,0～5 cm的净硝化速率和净氮矿化速率显著高于其余3层,增雨和减雨处理的净硝化速率和净氮矿化速率显著高于对照.研究结果说明降水变化对土壤铵态氮及氨化作用 的影响弱于对硝态氮及硝化作用的影响,这有助于更准确地评估降水变化对人工林生态系统服务功能和氮素生物地球化学循环过程的影响.
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| [51] |
Rate of aerobic nitrogen transformations in six acid climax forest soils and the effect of phosphorus and CaCO3. |
| [52] |
Nitrogen mineralization in soils under grasses and under trees in a protected Venezuelan savanna. https://doi.org/10.1097/01.mco.0000247475.95026.a5 URL [本文引用: 1] 摘要
Nitrogen mineralization was evaluated in soils beneath the most common woody species growing isolated within the grass matrix of a Venezuelan Trachypogon savanna, which has been protected from fire and cattle grazing since 1961. Adult trees of three evergreen species, Byrsonima crassifolia (L) H. B. K., Curatella americana L., and Bowdichia virgilioides H. B. K; and two deciduous, Godmania macrocarpa Hemsley and Cochlospermun vitifolium (Wild) Spreng were selected. The amount of N mineralized (NH4+-N + NO3--N) during 15 weeks of laboratory incubation of soils collected from beneath trees, was significantly higher (p < 0.01) than those from under grasses. Values of N mineralized on soil from under trees were from 21.28 to 82.65% greater than for soil from under grasses. A highly significant (p < 0.01) positive correlation, for all soils, was found between Nm and SOC, and between Nm and Nt. The higher N mineralization rates under trees would reflect a higher soil biological activity, due to higher SOC and NI, of the soils under the tree canopies then those under grasses. The N availability values obtained under all species reveal the importance these trees have for creating enriched areas on generally oligotrophic soils. Nitrogen mineralized in the soil from beneath evergreen trees was significantly (p < 0.01) higher than from under deciduous trees, being 25.87% higher on average. Similarly to the relation found for all soils, a highly significant (p < 0.01) positive correlation between Nm and SOC and between Nm and Nt was also obtained for soils beneath all trees, indicating the importance of SOC and Nt for nitrogen mineralization processes in this savanna. The higher SOC and Nt contents found under evergreen trees are probably due to the longer time they have been established on the site as compared to the deciduous ones. The chemical quality of fresh fallen leaves (as measured by their lignin/nitrogen ratio) did not seem to influence the quality of the
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| [53] |
Relationship between mineral N content and N mineralization rate in disturbed and undisturbed soil samples incubated under field and laboratory conditions. https://doi.org/10.1071/SR9920477 URL [本文引用: 1] 摘要
Soil Research is an international journal of soil science publishing high quality research on: soil genesis, soil morphology and classification; soil physics and hydrology; soil chemistry and mineralogy; soil fertility and plant nutrition; soil biology and biochemistry; soil and water management and conservation; soil pollution and waste disposal
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| [54] |
Soil nitrogen net mineralization and nitrification in typical Calamagrostis angustifolia wetlands in Sanjiang Plain. 三江平原典型小叶章湿地土壤氮素净矿化与硝化作用 . |
| [55] |
Phosphorus acqui- sition and use: Critical adaptations by plants for securing a nonrenewable resource. |
| [56] |
An extraction method for measuring soil microbial biomass C. https://doi.org/10.1016/0038-0717(87)90052-6 URL [本文引用: 1] 摘要
We propose that the organic C rendered extractable to 0.5 m K 2 SO 4 after a 24 h CHCl 3 -fumigation ( E C ) comes from the cells of the microbial biomass and can be used to estimate soil microbial biomass C in both neutral and acid soils.
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| [57] |
Terrestrial phosphorus limitation: Mechanisms, implica- tions, and nitrogen-phosphorus interactions. |
| [58] |
Nitrogen and carbon mineraliza- tion of semi-arid shrubland soil exposed to long term atmospheric nitrogen deposition. https://doi.org/10.1007/s00374-006-0137-y URL Magsci [本文引用: 2] 摘要
<a name="Abs1"></a>Anthropogenic N-deposition represents a significant input of N into semi-arid chaparral and coastal sage scrub (CSS) shrublands of southern California. High levels of atmospheric N deposition have the potential to increase soil C and N mineralization, and we hypothesize that semi-arid shrubland soil exposed to long-term (decades) high N deposition will have significantly higher C and N mineralization potentials. This hypothesis was tested in a laboratory incubation where the inorganic N (NH<sub>4</sub>+NO<sub>3</sub>) and CO<sub>2</sub> production of soils maintained at a constant temperature of 25°C and a soil moisture of 0.25 g H<sub>2</sub>O/g (65% water-filled pore space) were sampled sequentially over a 50-week period. The temporal trend in cumulative C and N mineralization was well described by a first- and zero-order model, respectively. Long-term atmospheric N deposition significantly increased potential N mineralization but not C mineralization, and both the rate and total N mineralization were significantly positively correlated with the surface (0–10 cm) soil <i>δ</i> <sup>15</sup>N natural abundance and negatively correlated with the surface soil C:N ratio. While the incubation techniques used here do not provide realistic estimates of in situ C or N mineralization, these assays indicate that atmospheric N deposition has significantly altered ecosystem N storage and cycling.
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| [59] |
Nitrogen addition and mowing affect microbial nitrogen transformations in a C4 grassland in northern China. |
| [60] |
The effects of N and P additions on microbial N transformations and biomass on saline-alkaline grassland of Loess Plateau of Northern China. https://doi.org/10.1016/j.geoderma.2013.08.003 URL [本文引用: 8] 摘要
During the whole growing seasons, P addition significantly stimulated soil inorganic N pool, soil extractable C, soil extractable N pool, R min , and the metabolic quotient ( q CO 2 ) from the estimates of microbial respiration and microbial biomass carbon, and there was no effect on peak aboveground biomass, MBC, MBN and MR during the whole growing seasons in 2009. N addition significantly increased peak aboveground biomass, inorganic N pool, R min , MBN, MR, and q CO 2 , decreased soil extractable C and the ratio of MBC/MBN, and there was no effect on soil extractable N and MBC during the growing season in 2009. P addition increased the soil net N mineralization rate and N addition not only increased the soil net N mineralization rate but also increased microbial biomass N. We observed that P induced a decreased soil inorganic N pool, but N addition directly increased soil inorganic N pool, how to balance the quantity of N and P additions in agriculture system is an important technique in agriculture harvest in the future in Loess Plateau of Northern China.
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| [61] |
Temperature and soil moisture interactively affected soil net N mineralization in temperate grassland in Northern China. https://doi.org/10.1016/j.soilbio.2005.09.009 URL [本文引用: 1] 摘要
Intact soil cores from three adjacent sites (Site A: grazed, Site B: fenced for 4 years, and Site C: fenced for 24 years) were incubated in the laboratory to examine effects of temperature, soil moisture, and their interactions on net nitrification and N mineralization rates in the Inner Mongolia grassland of Northern China. Incubation temperature significantly influenced net nitrification and N mineralization rates in all the three grassland sites. There were no differences in net nitrification or N mineralization rates at lower temperatures (-10, 0, and 5 掳C) whereas significant differences were found at higher temperatures (15, 25, and 35 掳C). Soil moisture profoundly impacted net nitrification and N mineralization rates in all the three sites. Interactions of temperature and moisture significantly affected net nitrification and mineralization rates in Site B and C, but not in Site A. Temperature sensitivity of net nitrification and N mineralization varied with soil moisture and grassland site. Our results showed greater net N mineralization rates and lower concentrations of inorganic N in the grazed site than those in the fenced sites, suggesting negative impacts of grazing on soil N pools and net primary productivity.
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| [62] |
Net nitrogen mineralize- tion and nitrification in three subtropical forests of south- western China. |
| [63] |
Influence of phosphorus loading on organic nitrogen mineralization of everglades soils. https://doi.org/10.2136/sssaj2000.6441525x URL [本文引用: 2] 摘要
ABSTRACT There have been recent concerns about the anthropogenic phos- phorus (P) loading to the naturally oligotrophic Everglades ecosystem. We investigated the effect of P loading on the biogeochemical cycling of nitrogen (N). We investigated the distribution of the potentially mineralizable N (PMN) rate as an indicator of the influence of P loading on selected microbial activities in soil and detritus layers. Soil characteristics measured included bulk density; total C, N, and P; microbial biomass C; and N and extractable NH|. PMN rates ranged from 10.4 to 325 mg N kg"1 d"1. The highest values of microbial biomass C and N, total P, extractable NH|, and PMN were observed in the detrital layer, and rates decreased with increasing soil depth. An increase in the size of the microbial pool and heterotrophic activity (organic N mineralization) was found to be related to the P-loading rate and related to the distribution of total P content in the soil and detrital layers. Extractable NHJ was a good indicator of PMN rates and total P was found to be significantly correlated to microbial biomass C and N. The stimulatory effect of P enrichment on microbial activity, overall size of the microbial biomass pool, and the PMN rate has led to an increased availability of inorganic N, which could potentially affect macrophyte growth and water quality of the northern Everglades system.
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| [64] |
The problem and its possible solution of phosphorus nutrient of natural grass- land in Inner Mongolia. 内蒙古天然草地磷素营养问题及其解决途径 .
内蒙古天然草地土壤中速效磷含 量低,直接影响草群的磷素营养,绝大部分草地都表现缺磷,而且近年主要牧草的磷含量有明显的下降趋势,都会影响到放牧家畜的营养平衡,不利于草地畜牧业的 健康发展。合理利用草地、积极利用富磷牧草、适当增加磷肥投入、增加豆科牧草比重是改善内蒙古草地磷营养状况的有效措施。
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| [65] |
Significant soil acidification across northern China’s grasslands dur- ing 1980s-2000s. |
| [66] |
Substrate type, temperature, and moisture content affect gross and net N mineralization and nitrification rates in agroforestry systems. https://doi.org/10.1007/s00374-003-0716-0 URL [本文引用: 2] 摘要
Accurate prediction of soil N availability requires a sound understanding of the effects of environmental conditions and management practices on the microbial activities involved in N mineralization. We determined the effects of soil temperature and moisture content and substrate type and quality (resulting from long-term pasture management) on soluble organic C content, microbial biomass C and N contents, and the gross and net rates of soil N mineralization and nitrification. Soil samples were collected at 0–10cm from two radiata pine ( Pinus radiata D. Don) silvopastoral treatments (with an understorey pasture of lucerne, Medicago sativa L., or ryegrass, Lolium perenne L.) and bare ground (control) in an agroforestry field experiment and were incubated under three moisture contents (100, 75, 50% field capacity) and three temperatures (5, 25, 40°C) in the laboratory. The amount of soluble organic C released at 40°C was 2.6- and 2.7-fold higher than the amounts released at 25°C and 5°C, respectively, indicating an enhanced substrate decomposition rate at elevated temperature. Microbial biomass C:N ratios varied from 4.6 to 13.0 and generally increased with decreasing water content. Gross N mineralization rates were significantly higher at 40°C (12.9μg) than at 25°C (3.9μg) and 5°C (1.5μg g 611 soil day 611 ); and net N mineralization rates were also higher at 40°C than at 25°C and 5°C. The former was 7.5-, 34-, and 29-fold higher than the latter at the corresponding temperature treatments. Gross nitrification rates among the temperature treatments were in the order 25°C >40°C >5°C, whilst net nitrification rates were little affected by temperature. Temperature and substrate type appeared to be the most critical factors affecting the gross rates of N mineralization and nitrification, soluble organic C, and microbial biomass C and N contents. Soils from the lucerne and ryegrass plots mostly had significantly higher gross and net mineralization and nitrification rates, soluble organic C, and microbial biomass C and N contents than those from the bare ground, because of the higher soil C and N status in the pasture soils. Strong positive correlations were obtained between gross and net rates of N mineralization, between soluble organic C content and the net and gross N mineralization rates, and between microbial biomass N and C contents.
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| [67] |
N2O emission from the semi-arid ecosystem under mineral fertilizer (urea and superphosphate) and increased precipitation in northern China. |
| [68] |
Effects of nitrogen addition on net nitrogen mineralization in Leymus Chinensis grassland, Inner Mongolia, China. Chinese Journal of Plant Ecology, 33, 563‒569. (in Chinese with English abstract)氮素添加对内蒙古羊草草原净氮矿化的影响 .https://doi.org/10.3773/j.issn.1005-264x.2009.03.015 URL [本文引用: 2] 摘要
为了更好地了解天然草原氮素矿化对全球氮沉降背景和草原施肥管理模式的响应,从2000年起对内蒙古典型草原羊草（Leymu schinensis）群落开展了长期的氮素添加实验,分别设置对照（N0）,添加5gNH4NO3·m^–2（N1.75）、30gNH4NO3·m^–2（N10.5）和80gNH4NO3·m^–2（N28）4个氮素添加梯度。2002年,从相邻的同时进行施肥的两个生态系统类型,即1979年围封的样地A和1999年围封的样地B进行土壤取样,在最佳温度（25℃）和最适土壤湿度（即60%田间持水量）下进行5周的室内培养,并用阶段性淋溶方法研究了氮素添加对土壤氮矿化动态的影响。在A和B两个样地内,氮素添加都显著改变了土壤的累积氮矿化量。最高氮素处理N28对应于最低的累积氮矿化量,而低氮素处理N1.75使得累积氮矿化量达到最高。在N0和N1.75处理中,硝态氮的含量高于铵态氮;在N28处理中,却表现出相反的趋势。氮素添加显著降低了土壤的pH值,但累积氮矿化量与土壤pH值、有机碳和全氮均没有显著的相关性。大多数氮素添加处理水平在样地A具有比样地B更高的土壤累积氮矿化量。
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Effect of nitrogen fertilization on net nitrogen mineraliza- tion in a grassland soil, northern China. |
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Seasonal varia- tions in nitrogen mineralization under three land use types in a grassland landscape.
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| [71] |
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The effects of nitrogen addition on soil nitrogen mineralization in the semi-arid typical grassland of Loess Plateau. 氮素添加对黄土高原典型草原土壤氮矿化的影响 .https://doi.org/10.11733/j.issn.1007-0435.2014.03.005 URL Magsci [本文引用: 1] 摘要
<p>为了解氮沉降对黄土高原典型草原土壤氮矿化的影响，通过人工氮肥添加模拟试验，采用埋置PVC 管的树脂芯方法原位测定了土壤氮素净氨化、净硝化和净矿化量的季节变化规律，探讨了氮素添加初期对氮矿化/固持贡献量和硝态氮淋溶损失量的影响。结果表明：黄土高原典型草原土壤氮矿化以硝化作用为主，夏季净硝化速率显著高于秋季。氮添加初期改变了半干旱草地氮矿化的季节模式，夏季表现为氮固持，秋季表现为氮矿化，并增加了氮矿化/固持的变异度，氮添加和季节因素对土壤氮矿化/固持有显著的交互作用。氮添加初期高氮添加未抑制氮的矿化过程。夏秋2季树脂硝态氮的含量随模拟氮沉降强度增加而显著增加，但硝态氮淋失量小，仅占施氮量的1.72%～4.74%。</p>
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