凋落物是森林生态系统的重要组成部分, 凋落物的分解可为植物生长、微生物代谢提供营养物质与能量来源(Wang et al., 2017), 有研究(曾锋等, 2010)表明, 全球温度升高和凋落物碳的变化息息相关, 所以, 凋落物的分解问题也引起了人们的大量关注。早在1876年, 就有德国学者对凋落物的产生原因和它们的化学组成展开了深入研究, 并得出结论: 凋落物在养分循环中占据了十分重要的作用(林波等, 2004; 凌华等, 2009)。20世纪80年代后关于凋落物分解过程中木质素的促分解作用、多种营养元素的分解释放等问题有了大量研究(Berg & Ekbohm, 1991), 且研究对象也逐渐从多种凋落物转移到单种凋落物。微生物是凋落物分解过程中的重要驱动因子(闫鹏飞等, 2019)。微生物与凋落物分解之间的关系是凋落物研究领域的热点(宋影等, 2014)。而凋落物叶际微生物所呈现的不同数量、群落组成及功能代谢特征, 导致人们对凋落物分解过程的微生物机制认知不足。尤其是马尾松(Pinus massoniana)叶际微生物的研究还鲜有报道, 马尾松叶际微生物的多样性及功能尚不明确。对微生物在凋落物分解中所扮演的角色还没有达成普遍共识(黄锦学等, 2010; 陈亚梅等, 2015)。对森林凋落物的分解特征进行研究, 有助于全面认识陆地生态系统养分循环的过程及方式, 深入揭示森林生态系统结构和功能及改善森林土壤肥力。
传统意义上认为土壤微生物在凋落物的分解过程中发挥了主要作用。土壤微生物作为连接植物和土壤的重要生物因子, 不仅能通过产生各种酶水解和氧化凋落物, 而且能够进行氨化、硝化、固氮等过程, 改变凋落物的结构和化学组成(胡凯等, 2019)。 董学德等(2021)以麻栎(Quercus acutissima)-刺槐(Robinia pseudoacacia)混交林和麻栎纯林为研究对象, 对凋落物分解过程中土壤微生物菌群多样性特征及其对凋落物分解速率的影响进行了研究。结果表明: 土壤微生物群落对麻栎-刺槐混交林和麻栎纯林凋落物分解速率具有重要影响。孟盈盈等(2021)以陌上菅(Carex thunbergii)为研究对象, 分析叶片凋落物和细根在不同土壤水分含量下的分解动态。结果表明: 湿地水位变化条件下, 土壤水分含量对细根和叶片凋落物分解具有不同的影响, 土壤水分含量的增加促进了叶片凋落物的分解, 但对细根的分解产生了抑制作用。
近些年有关叶际微生物的研究成果表明, 作为最先定殖在凋落物上的微生物, 叶际微生物可能在凋落物的分解中发挥了重要功能。叶际微生物, 即寄生或附生于植物叶表面和叶内部的微生物(Peñuelas & Terradas, 2014), 广义的叶际微生物还包括凋落叶(尚未接触土壤)所携带的微生物(Sadaka & Ponge, 2003)。通过分离培养的方法, Sadaka和Ponge (2003)发现Quercus rotundifolia的部分叶际真菌可以在凋落叶上定殖并伴随凋落叶的分解过程发生变化; Voříšková和Baldrian (2013)发现叶际真菌是参与凋落叶快速分解阶段的最主要的微生物类群; 运用高通量测序技术, Tláskal等(2016)发现Quercus petraea叶际细菌群落中的部分物种可以在凋落叶中定殖, 并可能参与凋落叶的分解。Lindahl和Boberg (2008)发现松柏类植物的凋落叶叶际真菌能在落叶初期从老化菌丝体中转移氮营养来克服氮缺乏, 从而促进自身生长。然而, 将叶际微生物群落作为整体, 叶际微生物对凋落叶的分解能力还是未知的。
1 材料和方法
1.1 研究区概况
本研究样地位于贵州省黔南州龙里县国有林场25年生马尾松纯林(26.47° N, 107.01° E)。样地平均海拔997 m, 土壤以黄壤为主: pH 4.4, 有机质含量21.46 g·kg-1, 总氮含量0.68 g·kg-1, 有效氮含量62.20 mg·kg-1, 总磷含量0.11 g·kg-1, 有效磷含量 0.86 mg·kg-1, 有效钾含量62.70 mg·kg-1 (李敏等, 2016)。该区域属亚热带湿润季风气候, 年平均气温13.6-19.6 ℃, 年降水量1 028.6-1 432.9 mm。
1.2 样品及土壤采集
凋落物样品采集: 于2019年12月, 在样地内设置4个20 m × 20 m的样方, 样方间距50 m以上。在各样地内分别布设20个1 m × 1 m的凋落物收集网(1 mm孔径的尼龙网), 收集网距地面40 cm, 由木桩支撑四角, 防止凋落针叶与土壤接触, 使用凋落物收集网收集7天内凋落的针叶(大约2 kg)带回实验室, 将其剪成5 cm长片段。取100 g针叶(每个样品20 g, 5个重复) 80 ℃烘干至恒质量后进行干质量换算, 另取部分未烘干针叶进行针叶形态观察。
微生物多样性样品采集: 根据周政贤(2001)的研究结果, 速生期马尾松的针叶生物量集中在第5到8盘的2-3年生枝条, 为使采集的样品更具代表性, 从树冠中部(树冠底部向上2 m左右)收集针叶。具体采集过程为: 在样地内随机选取15株马尾松, 间距10 m以上。使用高枝剪(15 m)采集马尾松针叶, 按不同方位采集, 每株采集约10 g健康成熟针叶(NM) (剔除已枯死但并未凋落针叶), 将采集的针叶每5株混为1个样品。用凋落物收集网收集7天内凋落的针叶(L), 并同时采集林地地表分解层针叶(F), 各采集15份, 每5份混合作为一个样品。
土壤采样: 于样地内设置4个20 m × 20 m的样方, 以马尾松林地表层土壤(0-10 cm)为土壤样品, 采用多点混样法进行土壤采集。采样前小心除去地表枯落物, 将所有土样充分混合均匀, 放入密封袋, 运回实验室, 立即去除动植物残体和石砾等杂质。
1.3 凋落物室内分解实验
在20 ℃ (马尾松生长季的平均温度)、空气相对湿度80%条件下于培养箱内进行室内分解实验(暗培养), 设置叶际微生物+土壤微生物(N+S); 叶际微生物+灭菌土壤微生物(N+SS); 灭菌叶际微生物+土壤微生物(SN+S) 3个处理。根据实验设置的不同, 对土壤微生物进行如下处理: 对N + SS的待用土壤进行高压蒸汽灭菌。对SN + S和N + S待用土壤不进行处理。对凋落针叶进行如下处理: 对SN + S待用针叶进行高压蒸汽灭菌; 对N + SS和N + S待用针叶不进行处理。分解实验使用方形组培瓶(120 mm × 120 mm × 120 mm)进行, 在无菌组培瓶中装入直径10 cm高5 cm的马尾松纯林表层土(添加无菌水调整含水量至70%田间持水量), 随后均匀覆盖5 g马尾松针叶。
每处理各40瓶, 根据水分损耗情况(不考虑凋落物分解过程中由于微生物的代谢导致的有机物质量损失, 该质量损失相对于培养瓶体系的整体质量而言可忽略不计), 每月向培养瓶内补充无菌水1次(于超净台内用无菌注射器注入)。
1.4 凋落物分解测定
在实验开始后的第2、4、8、12个月每处理分别随机取样测定凋落物分解情况。测试指标包括凋落针叶形态, 质量损失情况, 纤维素、木质素含量, 胞外酶活性。
(1)针叶形态特征观测: 随机挑取几根松针, 剪成1 cm长的片段后用导电胶带粘贴在样品台上, 用离子溅射仪(MSP-mini, 上海普金电气科技有限公司, 上海)镀金1 min。扫描电子显微镜(SEM) (TM 4000 plus, Hitachi, Tokyo, Japan)观测条件为: 低真空, 15 kV, 背散射电子成像。
(2)针叶质量损失率测定: 定期对组培瓶内针叶进行取样(实验开始后2、4、8、12个月), 取约1 g鲜针叶, 刷去表面附着土壤, 称针叶鲜质量。烘干, 计算含水率, 换算针叶总干质量, 进一步换算针叶质量损失率(Olson, 1963)。凋落针叶质量损失率由以下公式计算: 凋落针叶质量损失率(%) = Xt/X0 × 100%。X0为凋落针叶初始干质量, Xt为分解t时间后针叶质量损失量。
(3)纤维素、木质素含量测定: 分别采用Solarbio纤维素(CLL)含量检测试剂盒和Solarbio木质素含量检测试剂盒测定针叶纤维素和木质素含量, 并换算纤维素和木质素质量损失率(春敏莉等, 2009)。凋落针叶纤维素及木质素质量损失率由以下公式计算: 凋落针叶纤维素和木质素损失率(%) = xt/x0 × 100%。x0为凋落针叶初始纤维素或木质素含量, xt为分解t时间后针叶纤维素或木质素质量损失量。
(4)胞外酶活性测定: 采用Solarbio多酚氧化酶(PPO)含量检测试剂盒、Solarbio过氧化酶(POD)含量检测试剂盒、Solarbio β-葡萄糖苷酶(β-GC)含量检测试剂盒、Solarbio纤维二糖苷酶(C1)含量检测试剂盒测定针叶多酚氧化酶、过氧化物酶、β-葡萄糖苷酶、纤维二糖苷酶活性。
1.5 微生物多样性分析
采用PowerSoil DNA isolation kit试剂盒提取叶表微生物收集物的DNA, 分别使用带DNA片段的515F + 907R和ITS5 + ITS2引物对细菌16S V4-V5区和真菌ITS1区序列进行扩增纯化, 并构建文库。基于novaseq 6000平台对原来的数据进行了拼接、质控和嵌入式过滤等操作, 获得适用于随时检测和处理的有效数据进行高通量测序分析。使用Uparse软件以97%的频率一致性把有效的数据序列集合聚类为最邻近的可操作分类单元(OTUs), 筛选OTUs中出现频率最高的数据序列作为OTUs的一个代表。
物种注释: 对OTUs序列进行物种注释, 基于MUSCLE软件对细菌和真菌进行快速多序列比对, 获得所有OTUs代表序列的系统发生关系, 并在各分类水平统计各样本的群落组成, 最后以样本中数据量最少的为标准对各样本的数据进行均一化处理。
多样性分析: 基于Qiime软件进行OTUs数、Chao1、香农-威纳多样性指数(Shannon-Wiener diversity index)等α多样性指数和加权UniFrac距离(weighted Unifrac distance)计算, 并构建非加权配对算数平均法(UPGMA)样本聚类树; 使用R 2.15.3软件绘制叶表微生物的测定物种指数稀释曲线, 进行α多样性指数组间差异分析。
1.6 数据处理
采用Excel 2016对所有数据进行整理汇总, 利用SPSS 23.0软件对数据进行方差分析及相关性分析, 数据间的显著性分析采用最小显著性差异法(LSD) (p < 0.05)。
2 结果和分析
2.1 马尾松叶际微生物多样性
2.1.1 细菌多样性
通过对Reads拼接、质控、去嵌合体, 共得到536 490条有效序列。以97%的一致性将序列聚类成为OTUs, 去除低频序列后494 712条序列共聚类成2 468个OTUs。通过与数据库Silva 132比对, 进行物种注释, 并对不同分类层级统计发现: 注释到界水平的比例为100.00%, 门水平为99.69%, 纲水平为98.21%, 目水平为97.42%, 科水平为48.77%, 属水平为19.07%, 种水平为9.42%。
图1
图1
细菌(A)及真菌(B)优势目在不同马尾松针叶样品中的分布情况。F、L、NM分别表示分解层针叶、凋落针叶和成熟针叶。
Fig. 1
Distribution of dominant orders of bacteria (A) and fungi (B) in different needle samples of Pinus massoniana. F, L, NM represent the needles of decomposition layer, litter, mature, respectively.
图2
图2
马尾松凋落针叶(L)、成熟针叶(NM)和分解层针叶(F)的韦恩图。数字代表可操作运算分类单元数。
Fig. 2
Venn diagram of littered needles (L), mature needles (NM), and decomposed needles (F) of Pinus massoniana. Arabic numbers represent the number of operational taxonomic units.
2.1.2 真菌多样性
通过对Reads拼接、质控、去嵌合体, 共得到468 752条有效序列。以97%的一致性将序列聚类成为OTUs, 去除低频序列后461 014条序列共聚类成1 555个OTUs。通过与数据库UNITE比对, 进行物种注释, 并对不同分类层级统计发现: 能够注释到界水平的比例为100.00%, 门水平为81.19%, 纲水平为75.84%, 目水平为74.00%, 科水平为59.85%, 属水平为46.50%, 种水平为31.06%。
2.2 马尾松凋落针叶形态
随分解时间的延长, 各处理下凋落针叶表面定殖的微生物逐渐增多, 针叶表面逐步分解, 其内部细胞结构趋于破碎化(图3)。以叶际微生物+土壤微生物(N+S)处理为例, 在2个月时, 针叶外表面发现大量微生物定殖(图3A, 3E), 在4-8个月, 针叶表面定殖微生物不断增多并伴随形态持续破损(图3B、3C、3F、3G), 在12个月时, 针叶表面及内部均被大量微生物分解, 细胞壁出现严重破损, 细胞边界已无法分辨(图3H)。整体来看, N+S处理下针叶分解最快, 在8个月时针叶表面已明显被侵蚀, 针叶内部细胞难以分辨; 相较而言, 叶际微生物(N+SS)处理在8个月(图3G1), 土壤微生物(SN+S)处理在12个月(图3H2)时针叶内部细胞仍清晰可见, 同时这两个处理的针叶表面也仅在12个月时有明显侵蚀痕迹。
图3
图3
不同分解时期马尾松针叶形态。图A-D分别代表N+S处理下第2、4、8、12个月时针叶的外部形态，图E-H分别代表N+S处理下第2、4、8、12个月时针叶的解剖结构；图A1-D1分别代表N+SS处理下第2、4、8、12个月时针叶的外部形态，图E1-H1分别代表N+SS处理下第2、4、8、12个月时针叶的解剖结构；图A2-D2分别代表SN+S处理下第2、4、8、12个月时针叶的外部形态，图E2-H2代表SN+S处理下第2、4、8、12个月时针叶的解剖结构。N+S、N+SS、SN+S分别表示叶际微生物+土壤微生物、叶际微生物和土壤微生物3种处理。比例尺= 50 μm。
Fig. 3
Morphological changes of Pinus massoniana needles at different decomposition stages. A-D show the surface morphologies of needles in N+S treatment after 2, 4, 8 and 12 months, respectively. E-H show the anatomical structures of needles in N+S treatment after 2, 4, 8 and 12 months, respectively; A1-D1 show the surface morphologies of needles in N+SS treatment after 2, 4, 8 and 12 months, respectively. E1-H1 show the anatomical structures of needles in N+SS treatment after 2, 4, 8 and 12 months, respectively; A2-D2 show the surface morphologies of needles in SN+S treatment after 2, 4, 8 and 12 months, respectively. E2-H2 show the anatomical structures of needles in SN+S treatment after 2, 4, 8 and 12 months, respectively.N+S、N+SS、SN+S represent the phyllospheric microbes + soil microbes treatment, the phyllospheric microbes treatment and the soil microorganism treatment, respectively. Scale bars = 50 μm.
2.3 不同处理下马尾松凋落针叶的分解情况
整体而言, 随培养时间的延长, 各处理下凋落针叶质量损失均呈现由快转慢的趋势(图4)。在培养的前8个月, 凋落针叶质量损失较快, 各处理不同时间点间质量损失率差异显著; 8个月后, 凋落针叶质量损失减缓, 各处理8个月与12个月间质量损失均无显著差异。不同处理下凋落针叶质量损失存在差异。在培养2个月时, 3个处理间凋落物的质量损失率无显著差异; 第4个月时SN+S处理相较于其他两个处理, 凋落针叶质量损失显著降低; 培养8个月时SN+S处理和N+SS相较于N+S处理, 凋落针叶质量损失率显著降低; 培养12个月时SN+S处理相较于其他两个处理, 凋落针叶质量损失率显著降低。
图4
图4
不同处理下马尾松凋落针叶的分解情况(平均值±标准差)。 N+S、N+SS、SN+S分别表示叶际微生物+土壤微生物、叶际微生物和土壤微生物3种处理。不同大写字母代表同一时间不同组间差异显著(p < 0.05), 不同小写字母表示不同时间组内差异显著(p < 0.05)
Fig. 4
Decomposition of Pinus massoniana leaf litter under different treatments (mean ± SD). N+S、N+SS、SN+S represent the phyllospheric microbes + soil microbes treatment, the phyllospheric microbes treatment and the soil microorganism treatment, respectively. Different uppercase letters represent significant differences among different treatments at the same time point, and different lowercase letters represent significant differences among the same treatment at different time points (p < 0.05).
不同处理下凋落针叶木质素质量损失存在较大差异。随培养时间延长, N+SS和SN+S处理下木质素质量损失均呈现先慢后快趋势, 其中, N+SS处理在培养的前2个月分解较慢, 随后分解速率加快, 在2至12个月内无明显下降趋势; SN+S处理在培养的前4个月分解较慢, 随后分解速率加快, 8个月以后分解速率再次放缓。相较而言, N+S处理下木质素分解速率最高, 且在培养的第8个月及第12个月其质量损失率显著高于其他处理。
随培养时间的延长, 不同处理下凋落针叶纤维素质量损失均呈现先快后慢的趋势, 且不同处理间差异较小。整体来看, N+S处理下纤维素分解速率最快, 在12个月时其纤维素质量损失率均显著高于其他处理。
2.4 马尾松凋落针叶酶活性
图5
图5
马尾松凋落针叶酶活性(平均值±标准差)。N+S、N+SS、SN+S分别表示叶际微生物+土壤微生物、叶际微生物和土壤微生物3种处理。不同大写字母为同一时间不同组间差异显著(p < 0.05), 不同小写字母表示不同时间组内差异显著(p < 0.05)
Fig. 5
Enzyme activity of Pinus massoniana leaf litter (mean ± SD). N+S, N+SS and SN+S represent treatment groups of phyllospheric microorganisms + soil microorganisms, phyllospheric microorganisms and soil microorganisms, respectively. Different uppercase letters represent significant differences among different treatments at the same time point, and different lowercase letters represent significant differences among the same treatment at different time points (p < 0.05).
相关分析结果表明, 凋落物针叶质量损失率与木质素质量损失率、纤维素质量损失率分别呈极显著正相关关系, 木质素质量损失率与纤维素质量损失率也呈极显著正相关关系, 多酚氧化酶活性与过氧化物酶活性、β葡萄糖苷酶活性分别呈极显著负相关关系, 过氧化物酶活性与β葡萄糖苷酶活性呈极显著正相关关系, β葡萄糖苷酶活性与纤维二糖苷酶活性呈极显著正相关关系, 纤维二糖苷酶活性与纤维素质量损失率呈显著负相关关系(表1)。
表1 马尾松凋落针叶不同指标相关性分析
Table 1
| 针叶质量损失率 Mass loss rate of needles | 多酚氧化酶活性 Polyphenol oxidase activity | 过氧化物酶活性 Peroxidase activity | β葡萄糖苷酶活性 β glucosidase activity | 纤维二糖苷酶活性 Fibrodisosidase activity | 木质素质量损失率 Mass loss rate of lignin | 纤维素质量损失率 Mass loss rate of cellulose | |
|---|---|---|---|---|---|---|---|
| 针叶质量损失率 Mass loss rate of needles | 1.000 | ||||||
| 多酚氧化酶活性 Polyphenol oxidase activity | 0.051 | 1.000 | |||||
| 过氧化物酶活性 Peroxidase activity | -0.013 | -0.368** | 1.000 | ||||
| β葡萄糖苷酶活性 β glucosidase activity | -0.089 | -0.354** | 0.314** | 1.000 | |||
| 纤维二糖苷酶活性 Fibrodisosidase activity | -0.107 | -0.016 | 0.148 | 0.462** | 1.000 | ||
| 木质素质量损失率 Mass loss rate of lignin | 0.868** | 0.094 | -0.025 | -0.077 | -0.187 | 1.000 | |
| 纤维素质量损失率 Mass loss rate of cellulose | 0.455** | 0.060 | 0.114 | -0.145 | -0.208* | 0.442** | 1.000 |
*, p < 0.05;**, p < 0.01.
3 讨论
微生物多样性分析结果显示马尾松叶际微生物有较高的物种多样性, 整体来看, 细菌的多样性高于真菌, 这与其他人的研究结果(Bailey et al., 2006)一致。成熟针叶与凋落针叶(衰亡针叶)叶际微生物组成差异较大, 这可能与生活态针叶与衰亡针叶微环境不同有关(叶际微生物从生活态针叶可直接获取的有机物相对有限) (Osono, 2002; Yao et al., 2019)。值得注意的是, 成熟针叶、凋落针叶和分解层针叶含有大量共有OTUs, 这些共有OTUs可能均来源于成熟针叶叶际微生物群落且可能具有重要生态功能, 如调控马尾松生长, 参与马尾松凋落针叶分解等(Sun et al., 2021)。
已有研究陆续从多种植物叶际分离到具有木质素或纤维素分解功能的微生物, 并在纯培养条件下验证了这些微生物对凋落物的分解功能(Crawford, 1978)。有研究表明, 植物叶内生真菌可参与凋落叶的分解过程(Müller et al., 2001), 部分内生真菌被证明具有分解木质素和高分子碳水化合物的能力(Osono & Takeda, 2001)。陈晏等(2010)发现外源施加叶内生真菌可明显加快茅苍术(Atractylodes lancea)凋落物中纤维素和木质素的降解。本研究中检测到的叶际微生物(特别是优势类群, 如变形菌门(Proteobacteria)细菌及担子菌门(Basidiomycota)真菌)可能同样具备凋落叶的分解功能。事实上, 已有研究发现, 在日本落叶松(Larix kaempferi)枯落叶(松针)分解过程中, 质量损失率的变化主要由担子菌引起, 担子菌能使木质素、碳水化合物产生不同比例的损失(Osono et al., 2003)。而变形菌门则是凋落物分解中的优势细菌类群(Delmotte et al., 2009), 该微生物类群代谢类型多样, 在叶际具有甲基营养、硝化、固氮和不产氧光合作用等多种功能(Watanabe et al., 2016), 很可能这类微生物在凋落叶分解中同样发挥重要功能。
各处理中, 以N+S处理的分解速率最快, 表明在凋落物分解方面叶际微生物与土壤微生物存在协同效应, 这验证了Austin等(2014)的猜想。很可能在叶际和土壤中参与分解凋落针叶的微生物类群不同且在功能上存在互补关系。另外, 由于叶际微生物的代谢适应过程, 即由共生、附生转为腐生需要时间(杨宽等, 2021), 另外土壤微生物对凋落针叶的定殖也需要时间(庾琴等, 2008), 因而N+SS处理及SN+S处理凋落针叶分解速率相对较慢。同时, 针叶扫描电镜观测结果也同样显示N+S处理下针叶细胞壁分解最快。作为纤维素和木质素的主要来源, 细胞壁的分解会使扫描电镜下细胞间界限不清, 难以分辨, 表明凋落物形态变化对凋落物的分解程度有一定的指示作用, 这与前人的研究结论(Dresbøll & Magid, 2006; 田晓堃, 2020)一致。
马尾松凋落针叶的分解过程可划分为快速分解期(前8个月)和缓慢分解期(8个月以后) 2个阶段, 这与陆晓辉(2017)的研究结果一致。作为凋落针叶的主要成分, 木质素和纤维素的分解速率与凋落针叶的质量损失直接相关。整体来看, 纤维素分解速率快于木质素, 在8个月时超过80%的纤维素已分解(N+S处理), 后续凋落针叶质量损失主要源于木质素的分解, 因而凋落针叶分解过程进入缓慢分解期。木质素和纤维素的分解主要受胞外酶活性的控制(Sinsabaugh et al., 1991)。陈明蓉等(2020)的研究表明, 在凋落物分解前期, 内生真菌定殖可提高过氧化物酶活性, 在本研究中, 过氧化物酶在前期的活性较高, 很可能与内生真菌的定殖有关。在本研究中, 木质素分解酶——多酚氧化酶活性与过氧化物酶活性变化呈相反趋势, 这可能与两者在多酚类化合物分解中存在时序性有关(胡凯等, 2021)。整体来看, 这两种酶的活性相对不高且在不同处理间差异不大, 这与木质素难以分解(张雨鉴等, 2020; 郭绮雯等, 2021)且木质素分解微生物在土壤和叶际环境中均有分布有关(Sun et al., 2021)。另外, 这两种酶的活性与木质素分解率无显著相关关系。事实上, 胞外酶活性仅能部分决定凋落物的分解速率(Allison & Vitousek, 2004)。作为纤维素分解的起始酶, 纤维二糖苷酶活性变化与纤维素的分解率极显著相关, 这与以往的研究结果(孙思琦, 2020; 许从峰等, 2020; 王明, 2021; 杨梦雅等, 2021)相同。整体来看, 3个处理中, SN+S处理下纤维素分解酶——β葡萄糖苷酶和纤维二糖苷酶的活性变化相对滞后, 这可能受土壤微生物对凋落针叶的定殖及代谢适应需要时间有关(朱蔚娜等, 2021; 李勋等, 2022; 张磊等, 2022)。
4 结论
本研究发现马尾松针叶在凋落后其携带的叶际微生物群落发生改变, 且成熟针叶、凋落针叶、分解层针叶共有大量OTUs, 室内分解实验进一步验证了马尾松叶际微生物(衰亡针叶叶际微生物)可直接参与凋落针叶的分解, 且在凋落针叶的分解过程中叶际微生物与土壤微生物有协同作用。这些结果对进一步阐明凋落物的分解机制及后续发掘马尾松核心微生物组有重要指导意义。
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川西高山林线交错带两种地被物分解的木质纤维素酶活性特征
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Research progress of litter decomposition enzyme
凋落物分解酶的研究进展
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为深入理解进入凋落物层生长的林下植物根系对森林凋落物分解的影响,本研究通过分解袋模拟试验探讨不同生物量多花黑麦草根系对中亚热带常绿阔叶林优势树种四川山矾凋落叶分解中微生物及酶活性的影响.结果表明: 在分解的240 d进程中,无根(N)、少根(L)、多根(M)3种处理下凋落叶表面细菌和真菌群落多样性指数均表现为多根＞少根＞无根处理,并且不同根生物量处理对真菌群落组成和数量的影响较细菌更为显著.随着多花黑麦草生长季结束,生长进入分解袋中的活根生物量逐渐减少,根系对真菌群落组成的影响减小.同一分解阶段,凋落叶表面酸性磷酸酶、β-葡萄糖苷酶、多酚氧化酶、过氧化物酶活性在有根条件下均高于无根条件.表明根系的生长能够改变微生物群落组成与数量,并提高微生物胞外酶活性,从而对分解产生促进作用.
Controlling factors of litter decomposition rate in China’s forests
中国森林凋落物分解速率影响因素分析
Plant diversity and soil enzyme activity in 4 typical communities of Pinus massoniana in Guizhou
贵州马尾松群落植物多样性与土壤酶活性
Effects of mixed leaf litter on nitrogen and phosphorus release in Pinus massoniana and native broad-leaved tree species
马尾松与乡土阔叶树种凋落叶分解氮磷释放的混合效应
Advances in the studies of forest litter
In this paper, the authors presented the concepts of forest litter as well as the methodology and main subjects in the study of forest litter, especially the issues regarding litter gathering, aperture sizes of decomposition bags, spatial and temporal dynamics of litterfall and decomposition rates. Some important achievements in the studies of forest litter included influencing the factors of litterfall and decomposition process. Through reallocation of light, temperature and moisture, altitude and latitude affected litterfall globally. the leading influencing climatic factor was annual mean temperature. Decomposition rate of litters was correlated to their chemical composition and environmental factors. C/N ratio and the content of N played an important role in the process of litter decomposition. Soil moisture was a key environmental factor affecting litter decomposition. For the soil microbes, their effects on decomposition of litters fell into two stages. In the first stage, the microbes fragmented the surface layer of litters, which resulted in small animals entering into litters. While in the later stage, decomposition was mainly caused by breaking down of organic matters by microbes. In the future, studies will be concentrated on the factors influencing litterfall and decomposition as well as the ecological functioning of forest litters.
森林凋落物研究进展
对森林凋落物的概念、研究方法及主要研究内容作了阐述,特别就凋落物收集面积和分解袋孔径大小、凋落量时空动态和凋落物分解速率等问题进行了综合分析。目前森林凋落物研究的重要结论有:海拔和纬度因子是通过对光、温、水等生态因子的再分配来影响凋落量,其中主导气候因子是年均温。凋落物的分解与化学组成和环境因子有关,C/N和N含量在凋落物分解过程中起着重要作用。土壤水分是影响凋落物分解主要环境因子之一;土壤微生物对凋落物的影响,前期是通过真菌破碎凋落物表层使内居性动物得以侵入凋落物内部,后期则以细菌降解有机物为主。凋落量、凋落物分解的影响因子,以及凋落物的生态作用等内容应是凋落物研究的重要方向。
Controlling factors of litterfall in China’s forests
中国森林凋落量的影响因素
Effects of soil moisture content and litter quality on decomposition of Carex thunbergii fine roots and leaf litter
土壤水分含量和凋落物特性对陌上菅细根和叶片凋落物分解的影响
Diversity of endophytic fungi of single Norway spruce needles and their role as pioneer decomposers
The diversity of endophytic fungi within single symptomless Norway spruce needles is described and their possible role as pioneer decomposers after needle detachment is investigated. The majority (90%) of all 182 isolates from green intact needles were identified as Lophodermium piceae. Up to 34 isolates were obtained from single needles. Generally, all isolates within single needles had distinct randomly amplified microsatellite (RAMS) patterns. Single trees may thus contain a higher number of L. piceae individuals than the number of their needles. To investigate the ability of needle endophytes to act as pioneer decomposers, surface-sterilized needles were incubated on sterile sand inoculated with autoclaved or live spruce forest humus layer. The dry weight loss of 13-17% found in needles after a 20-week incubation did not significantly differ between the sterilized and live treatments. Hence, fungi surviving the surface sterilization of needles can act as pioneer decomposers. A considerable portion of the needles remained green during the incubation. Brown and black needles, in which the weight loss had presumably taken place, were invaded throughout by single haplotypes different from L. piceae. Instead, Tiarasporella parca, a less common needle endophyte, occurred among these invaders of brown needles. Needle endophytes of Norway spruce seem thus to have different abilities to decompose host tissues after needle cast. L. piceae is obviously not an important pioneer decomposer of Norway spruce needles. The diversity of fungal individuals drops sharply when needles start to decompose. Thus, in single needles the decomposing mycota is considerably less diverse than the endophytic mycota.
Energy storage and the balance of producers and decomposers in ecological systems
DOI:10.2307/1932179 URL [本文引用: 1]
Phyllosphere fungi on leaf litter of Fagus crenata: occurrence, colonization, and succession
DOI:10.1139/b02-028
URL
[本文引用: 1]
Phyllosphere fungi occur on various litters, but the ecology of these fungi on leaf litter has received little attention. To investigate the occurrence, colonization, and succession of phyllosphere fungi on leaf litter of Fagus crenata Blume, fungi were isolated from living, senescent, freshly fallen, and decomposing leaves by surface sterilization and washing methods. A total of 18 and 47 fungal species were isolated from the interior and surface of living and senescent leaves, respectively, and 15 frequent species were regarded as phyllosphere fungi. These fungi were divided into three groups according to their frequency on freshly fallen and decomposing leaves. Nine species (Group I) occurred frequently on decomposing leaves, two species (Group II) on freshly fallen leaves only, and four species (Group III) were frequent on living or senescent leaves only. Colonization of sterilized, freshly fallen leaves by phyllosphere fungi was investigated to test their ability to infect litter directly after litter fall. Frequencies of four species were lower on sterilized leaves than on unsterilized leaves, whereas frequencies of other species did not differ between sterilized and unsterilized leaves. Successional trends of endophytes and epiphytes were observed during decomposition from freshly fallen to decomposing leaves. The sum of frequencies of endophytes decreased temporarily on freshly fallen leaves and increased on decomposing leaves. The sum of frequencies of epiphytes decreased from freshly fallen to decomposing leaves.Key words: beech, decomposition, endophyte, epiphyte, Xylariaceae.
Roles of diverse fungi in larch needle-litter decomposition
Functional biodiversity of fungi in larch (Larix leptolepis) forests needle-litter decomposition was examined by a pure-culture test. Weight loss of larch-needle litter, utilization pattern of lignocellulose and chemical composition of remaining litter were investigated and compared for 31 isolates in 27 species of basidiomycetes and ascomycetes. Weight loss (% original weight) of litter ranged from -2.0% to 14.2%. Mean weight loss of litter caused by the basidiomycetes was not significantly different from that caused by the ascomycetes. Basidiomycetes caused loss of lignin and carbohydrates in variable proportions, while ascomycetes exclusively attacked carbohydrates without delignification. The content of lignin and nitrogen in remaining litter was not significantly correlated when both basidiomycetes and ascomycetes were included. However, the correlation coefficient was significant when the relationship was examined separately for basidiomycetes, indicating that the degree of selective delignification determined the final nitrogen content in litter. Possible effects of fungal colonization on needle-litter decomposition in larch forests are discussed.
Effects of organic chemical quality and mineral nitrogen addition on lignin and holocellulose decomposition of beech leaf litter by Xylaria sp.
DOI:10.1016/S1164-5563(01)01066-4 URL [本文引用: 1]
The foliar microbiome
DOI:10.1016/j.tplants.2013.12.007
PMID:24439491
[本文引用: 1]
Proficient performance in plants is strongly associated with distinct microbial communities that live in and on their organs. We comment here on the current knowledge of the composition of the foliar microbiome, highlight its importance for plants, ecosystemic functioning, and crop yields, and propose tools and experiments to overcome the current knowledge gap. Copyright © 2013 Elsevier Ltd. All rights reserved.
Fungal colonization of phyllosphere and litter of Quercus rotundifolia Lam. in a holm oak forest (High Atlas, Morocco)
DOI:10.1007/s00374-003-0666-6 URL [本文引用: 2]
An enzymic approach to the analysis of microbial activity during plant litter decomposition
DOI:10.1016/0167-8809(91)90092-C URL [本文引用: 1]
Dynamics of microbes and enzyme activities during litter decomposition of Pinus massoniana forest in mid-subtropical area
中亚热带马尾松林凋落物分解过程中的微生物与酶活性动态
Fungal diversity within the phyllosphere of Pinus massoniana and the possible involvement of phyllospheric fungi in litter decomposition
DOI:10.1016/j.funbio.2021.05.001 URL [本文引用: 2]
Bacterial succession on decomposing leaf litter exhibits a specific occurrence pattern of cellulolytic taxa and potential decomposers of fungal mycelia
DOI:10.1093/femsec/iw177 [本文引用: 1]
Fungal community on decomposing leaf litter undergoes rapid successional changes
DOI:10.1038/ismej.2012.116 [本文引用: 1]
Responses of litter decomposition and nutrient release rate to water and nitrogen addition differed among three plant species dominated in a semi-arid grassland
DOI:10.1007/s11104-017-3288-8 URL [本文引用: 1]
Microbial nitrification in throughfall of a Japanese cedar associated with Archaea from the tree canopy
DOI:10.1186/s40064-016-3286-y [本文引用: 1]
Synthetic microbial consortia for lignocellulosic biomass conversion
合成微生物群落用于木质纤维素生物质转化的研究进展
Effects of simulated warming and decomposition interface on the litter decomposition rate of Zizania latifolia and its phyllospheric microbial community structure and function
DOI:10.17521/cjpe.2018.0272 URL [本文引用: 1]
模拟增温及分解界面对茭草凋落物分解速率及叶际微生物结构和功能的影响
DOI:10.17521/cjpe.2018.0272
[本文引用: 1]
挺水植物的凋落物是湿地生态系统物质循环的重要组成部分, 阐明气候变暖以及生境差异对湿地挺水植物凋落物分解过程及叶际微生物的影响对揭示湿地生态系统关键物质循环过程具有重要意义。该研究以滇西北高原典型湿地优势挺水植物茭草(Zizania latifolia)为研究对象, 采用凋落物袋法研究了茭草在模拟增温(1.5-2.0 ℃)及不同生境(大气界面、水界面与土界面)下的质量残留率和叶际微生物数量、结构组成与功能代谢特征。研究发现: 模拟气候变暖及生境差异均显著影响凋落物的分解速率。经过一年的分解, 凋落物在模拟增温环境下的质量残留率为66.4%, 对照组的质量残留率为77.7%, 增温组分解常数(k)值是对照组的1.64倍, 而凋落物在水界面与土界面的质量残留率为42.2%和25.3%, 其k值分别为大气界面的3.63和5.25倍, 生境差异是影响湿地挺水植物凋落物分解速率的关键因素。模拟增温主要改变了凋落物叶际微生物的群落组成特征, 而生境变化主要影响叶际微生物的绝对数量、微生物多样性、群落结构组成以及功能代谢活性。处于土界面的凋落物叶际微生物具有最高的群落功能代谢活性及醇类碳源利用程度。不同处理之间的植物叶际微生物特征与凋落物分解速率具有较好的一致性, 为揭示湿地植物凋落物分解快慢的微生物驱动机制提供了重要的理论依据。
Advances in research on phyllosphere microorganisms and their interaction with plants
叶际微生物及与植物互作的研究进展
Decomposition characteristics of corn stover by microbial consortium PLC-8 with lignocellulose- degradation at low temperature
低温木质纤维素分解复合菌系PLC-8对玉米秸秆的分解特性
DOI:10.13304/j.nykjdb.2019.0841
[本文引用: 1]
为提高东北寒区玉米秸秆的分解效率，突破低温的瓶颈，探讨了低温木质纤维素分解复合菌系PLC-8对玉米秸秆的分解效果及其微生物多样性。通过pH、玉米秸秆的减重、木质纤维素的含量、酶活性、有机酸含量等指标评价玉米秸秆的分解效果，采用变性凝胶电泳（DGGE）和高通量测序技术研究其微生物多样性。结果表明：pH先下降后回升至接近初始值；30 d后，玉米秸秆减重率达到43.65%；半纤维素、纤维素、木质素含量分别减少了61.13%、40.91%、14.25%；纤维素酶活性先升高后降低，其中滤纸酶和β-葡萄糖苷酶活性在第20 d，分别为0.054、0.025 U·mL<sup>-1</sup>；内切酶和外切酶活性的最高值在第15 d，分别为0.032、0.030 U·mL<sup>-1</sup>；木聚糖酶活性随着玉米秸秆的分解而逐渐升高，甲酸和乙酸分别在第20和15 d达到最高值。微生物群落分析表明,PLC-8由细菌和真菌组成，具有分解稳定性，在属的水平上细菌优势菌株为金黄杆菌属（Chryseobacterium）、短波单胞菌属（Brevundimonas）、不动杆菌属（Acinetobacter）等，真菌的优势菌株为肉座菌（Hypocreales）。
Phyllosphere epiphytic and endophytic fungal community and network structures differ in a tropical mangrove ecosystem
DOI:10.1186/s40168-019-0671-0 [本文引用: 1]
Acetamiprid degradation by microbes of the soil and phyllosphere
土壤和叶际微生物对啶虫脒的降解作用
Review on forest litter decomposition
森林凋落物分解研究进展
DOI:10.16258/j.cnki.1674-5906(2010)01-0239-05 [本文引用: 1]
Effects of litter and root inputs changes on soil phosphorus fractions in a subtropical natural forest of Castanopsis carlesii
亚热带米槠天然林凋落物和根系输入变化对土壤磷组分的影响
Response of litter decomposition of zonal vegetation to simulated nitrogen deposition in central Yunnan, China
滇中亚高山地带性植被凋落物分解对模拟氮沉降的响应
Decomposition characteristics of leaf litters and roots of six main plant species and their relationships with functional traits in Stipa grandis steppe
DOI:10.17521/cjpe.2020.0268 URL [本文引用: 1]
大针茅草原6种主要植物叶凋落物和根系分解特征与功能性状的关系
