Uptake rate and preference of inorganic and organic nitrogen in roots of tree and shrub plants in Bashang, Hebei, China

doi:10.17521/cjpe.2023.0287

Abstract

Abstract:

Aims Understanding on how nitrogen uptake of plants is influenced by soil conditions and plant traits is crucial. Elucidating the nitrogen preferences of different plants and their interactions with soil properties and root traits, can enhance our understanding of plant nitrogen acquisition strategies. This knowledge can provide a theoretical basis for designing mixed-species plantation construction for arid and semi-arid region of northern China, like the Bashang region of Hebei Province.

Methods In Kangbao County, Zhangjiakou City, China, the tree species Ulmus pumila, Populus simonii, Caragana korshinskii, and Lycium barbarum were selected. The ¹⁵N isotope tracing technique was employed to quantify nitrogen uptake rates and preferences for different forms (nitrate, ammonium, and glycine) by these plants. Correlations among nitrogen uptake rates, root morphology, architecture, and chemistry, and soil characteristics were analyzed.

Important findings Lycium barbarum roots exhibited an uptake preference for nitrate with a contribution of 46.05%, followed by glycine and ammonium. For P. simonii, U. pumila, and C. korshinskii, the contributions of each form of nitrogen to total nitrogen uptake showed ammonium (44.91%-68.68%) > glycine (22.63%-45.11%) > nitrate (8.69%-9.98%). The nitrate uptake rate was significantly negatively correlated with root diameter and tissue density, but positively correlated with specific root length and specific surface area. This indicate that roots with smaller diameter, lower tissue density, larger specific root length, and greater specific surface area had higher nitrate uptake rate. Root branching intensity was positively correlated with the uptake rate of glycine and total nitrogen, suggesting that the roots with higher branching intensity take up organic and inorganic nitrogen more efficiently. Furthermore, there was a significant negative correlation between root nitrogen content and ammonium as well as glycine or total nitrogen uptake rate; implying that roots with lower nitrogen content displayed higher nitrogen uptake rate. The observed differences in the nitrogen uptake patterns among four species were influenced not only by soil nitrogen content but also by various morphological, architectural, and chemical traits of the roots. Based on the plant nitrogen uptake preference and relationships with root structural traits and soil fertility, it is necessary to minimize the interspecific competition of plants and maximize the use of nutrients in nutrient poor environment. Therefore, we recommended to construct a mixed-species shelterbelt such as tree-shrub combination (P. simonii - L. barbarum, U. pumila - L. barbarum) or shrub-shrub combination (C. korshinskii - L. barbarum), or to replant shrubs under the pure P. simonii or U. pumila plantations. These research results provide valuable insights for the constructing mixed-species shelterbelts in Bashang region of Hebei Province.

Key words: nitrogen uptake rate, nitrogen uptake preference, root trait, isotope labeling

LIU Qian-Yuan, YU Zhen-Dong, ZHANG Wei-Wei. Uptake rate and preference of inorganic and organic nitrogen in roots of tree and shrub plants in Bashang, Hebei, China[J]. Chin J Plant Ecol, 2024, 48(10): 1361-1373.

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Figures/Tables 8

References 57

[1]	Ashton IW, Miller AE, Bowman WD, Suding KN (2010). Niche complementarity due to plasticity in resource use: plant partitioning of chemical N forms. Ecology, 91, 3252-3260. PMID
[2]	Bloom AJ, Sukrapanna SS, Warner RL (1992). Root respiration associated with ammonium and nitrate absorption and assimilation by barley. Plant Physiology, 99, 1294-1301. DOI PMID
[3]	Bradford MA (2014). Ecology: good dirt with good friends. Nature, 505, 486-487.
[4]	Britto DT, Kronzucker HJ (2013). Ecological significance and complexity of N-source preference in plants. Annals of Botany, 112, 957-963. DOI PMID
[5]	Bueno A, Greenfield L, Pritsch K, Schmidt S, Simon J (2019). Responses to competition for nitrogen between subtropical native tree seedlings and exotic grasses are species-specific and mediated by soil N availability. Tree Physiology, 39, 404-416. DOI PMID
[6]	Dai LM (2020). A Study on Plants Nitrogen Uptake Preference Characteristics in Temperate Forests. Master degree dissertation, Northeastern University, Shenyang.
	[ 戴陆明(2020). 温带森林植物氮吸收偏好特性研究. 硕士学位论文, 东北大学, 沈阳.]
[7]	Dai SL (2008). Study on the Relationship Between Land Use and Soil Erosion in Kangbao County. Master degree dissertation, Capital Normal University, Beijing.
	[ 代士良 (2008). 康保县土地利用与土壤侵蚀关系研究. 硕士学位论文, 首都师范大学, 北京.]
[8]	Du E, Terrer C, Pellegrini AFA, Ahlström A, van Lissa CJ, Zhao X, Xia N, Wu X, Jackson RB (2020). Global patterns of terrestrial nitrogen and phosphorus limitation. Nature Geoscience, 13, 221-226.
[9]	Erktan A, McCormack ML, Roumet C (2018). Frontiers in root ecology: recent advances and future challenges. Plant and Soil, 424, 1-9.
[10]	Fay PA, Prober SM, Harpole WS, Knops JMH, Bakker JD, Borer ET, Lind EM, MacDougall AS, Seabloom EW, Wragg PD, Adler PB, Blumenthal DM, Buckley YM, Chu C, Cleland EE, et al. (2015). Grassland productivity limited by multiple nutrients. Nature Plants, 1, 15080. DOI: 10.1038/nplants.2015.80. PMID
[11]	Fu YX, Wang L, Peng S, Wang HY, Chang CP (2014). Research on windproof efficiency and type configuration of farmland shelterbelt in Bashang region of Hebei Province—Taking Kangbao County as an example. Research of Soil and Water Conservation, 21, 279-283.
	[ 付亚星, 王乐, 彭帅, 王红营, 常春平 (2014). 河北坝上农田防护林防风效能及类型配置研究——以河北省康保县为例. 水土保持研究, 21, 279-283.]
[12]	Gallet-Budynek A, Brzostek E, Rodgers VL, Talbot JM, Hyzy S, Finzi AC (2009). Intact amino acid uptake by northern hardwood and conifer trees. Oecologia, 160, 129-138. DOI PMID
[13]	Gao L, Cui X, Hill PW, Guo Y (2020). Uptake of various nitrogen forms by co-existing plant species in temperate and cold-temperate forests in northeast China. Applied Soil Ecology, 147, 103398. DOI: 10.1016/j.apsoil.2019.103398.
[14]	Gessler A, Schneider S, VON Sengbusch D, Weber P, Hanemann U, Huber C, Rothe A, Kreutzer K, Rennenberg H (1998). Field and laboratory experiments on net uptake of nitrate and ammonium by the roots of spruce (Picea abies) and beech (Fagus sylvatica) trees. New Phytologist, 138, 275-285. DOI PMID
[15]	Gu JC, Wang YN, Xiao LJ, Gao GQ (2019). Morphological and structural characteristics of 1-5 order roots in litter and soil horizons of Larix gmelinii Rupr. plantation. Journal of Northeast Forestry University, 47(4), 33-37.
	[ 谷加存, 王亚楠, 肖立娟, 高国强 (2019). 落叶松凋落物层和土壤层1-5级细根形态和结构特征. 东北林业大学学报, 47(4), 33-37.]
[16]	Holdaway RJ, Richardson SJ, Dickie IA, Peltzer DA, Coomes DA (2011). Species-and community-level patterns in fine root traits along a 120 000-year soil chronosequence in temperate rain forest. Journal of Ecology, 99, 954-963.
[17]	Hong J, Ma X, Yan Y, Zhang X, Wang X (2018). Which root traits determine nitrogen uptake by alpine plant species on the Tibetan Plateau. Plant and Soil, 424, 63-72.
[18]	Isaac ME, Borden KA (2019). Nutrient acquisition strategies in agroforestry systems. Plant and Soil, 444, 1-19. DOI
[19]	Ito T, Tanaka-Oda A, Masumoto T, Akatsuki M, Makita N (2023). Different relationships of fine root traits with root ammonium and nitrate uptake rates in conifer forests. Journal of Forest Research, 28, 25-32.
[20]	Jacob A, Leuschner C (2015). Complementarity in the use of nitrogen forms in a temperate broad-leaved mixed forest. Plant Ecology & Diversity, 8, 243-258.
[21]	Ji Y, Zhou G, Li Z, Wang S, Zhou H, Song X (2020). Triggers of widespread dieback and mortality of poplar (Populus spp.) plantations across Northern China. Journal of Arid Environments, 174, 104076. DOI: 10.1016/j.jaridenv.2019.104076.
[22]	Jia J, Li HY (2008). Resistance of several mixed plantation to Anoplophora nobilis. Journal of West China Forestry Science, 37(1), 82-85.
	[ 贾隽, 李红彦 (2008). 几种混交林对黄斑星天牛的抗虫性研究. 西部林业科学, 37(1), 82-85.]
[23]	Jiang Q, Guo RQ, Song TT, Chen TT, Chen YH, Jia LQ, Xiong DC, Chen GS (2020). Effects of warming and nitrogen addition on nitrogen uptake kinetics of fine roots of Cunninghamia lanceolata seedlings in different seasons. Acta Ecologica Sinica, 40, 2996-3005.
	[ 姜琦, 郭润泉, 宋涛涛, 陈廷廷, 陈宇辉, 贾林巧, 熊德成, 陈光水 (2020). 增温与氮添加对不同季节杉木幼苗细根不同形态氮吸收动力学的影响. 生态学报, 40, 2996-3005.]
[24]	Kahmen A, Livesley SJ, Arndt SK (2009). High potential, but low actual, glycine uptake of dominant plant species in three Australian land-use types with intermediate N availability. Plant and Soil, 325, 109-121.
[25]	Kong D, Ma C, Zhang Q, Li L, Chen X, Zeng H, Guo D (2014). Leading dimensions in absorptive root trait variation across 96 subtropical forest species. New Phytologist, 203, 863-872. DOI PMID
[26]	Li CC, Li QR, Xu XL, Ouyang H (2016). Nitrogen acquisition strategies of Cunninghamia lanceolata at different ages. Acta Ecologica Sinica, 36, 2620-2625.
	[ 李常诚, 李倩茹, 徐兴良, 欧阳华 (2016). 不同林龄杉木氮素的获取策略. 生态学报, 36, 2620-2625.]
[27]	Li X, Rennenberg H, Simon J (2016). Seasonal variation in N uptake strategies in the understory of a beech-dominated N-limited forest ecosystem depends on N source and species. Tree Physiology, 36, 589-600.
[28]	Liese R, Alings K, Meier IC (2017). Root branching is a leading root trait of the plant economics spectrum in temperate trees. Frontiers in Plant Science, 8, 315. DOI: 10.3389/fpls.2017.00315. PMID
[29]	Liese R, Lübbe T, Albers NW, Meier IC (2018). The mycorrhizal type governs root exudation and nitrogen uptake of temperate tree species. Tree Physiology, 38, 83-95. DOI PMID
[30]	Lipson D, Näsholm T (2001). The unexpected versatility of plants: organic nitrogen use and availability in terrestrial ecosystems. Oecologia, 128, 305-316. DOI PMID
[31]	Liu B, Li H, Zhu B, Koide RT, Eissenstat DM, Guo D (2015). Complementarity in nutrient foraging strategies of absorptive fine roots and arbuscular mycorrhizal fungi across 14 coexisting subtropical tree species. New Phytologist, 208, 125-136. DOI PMID
[32]	Liu M, Xu F, Xu X, Wanek W, Yang X (2018). Age alters uptake pattern of organic and inorganic nitrogen by rubber trees. Tree Physiology, 38, 1685-1693. DOI PMID
[33]	Liu QY, Chen YF, Chen YM, Wang HM (2023). Effects of different ammonium to nitrate ratios on nitrogen uptake preference and traits of absorptive roots of subtropical trees seedlings. Scientia Silvae Sinicae, 59(2), 48-57.
	[ 刘倩愿, 陈奕帆, 陈艳梅, 王辉民 (2023). 铵硝比对亚热带树种幼苗氮吸收偏好及吸收根属性的影响. 林业科学, 59(2), 48-57.]
[34]	Liu Q, Wang H, Xu X (2020). Root nitrogen acquisition strategy of trees and understory species in a subtropical pine plantation in Southern China. European Journal of Forest Research, 139, 791-804.
[35]	Liu Q, Xu M, Yuan Y, Wang H (2021). Interspecific competition for inorganic nitrogen between canopy trees and underlayer-planted young trees in subtropical pine plantations. Forest Ecology and Management, 494, 119331. DOI: 10.1016/j.foreco.2021.119331.
[36]	Ma Z, Guo D, Xu X, Lu M, Bardgett RD, Eissenstat DM, McCormack ML, Hedin LO (2018). Evolutionary history resolves global organization of root functional traits. Nature, 555, 94-97.
[37]	McKane RB, Johnson LC, Shaver GR, Nadelhoffer KJ, Rastetter EB, Fry B, Giblin AE, Kielland K, Kwiatkowski BL, Laundre JA, Murray G (2002). Resource-based niches provide a basis for plant species diversity and dominance in Arctic tundra. Nature, 415, 68-71.
[38]	Miller AE, Bowman WD (2002). Variation in nitrogen-15 natural abundance and nitrogen uptake traits among co-occurring alpine species: Do species partition by nitrogen form? Oecologia, 130, 609-616. DOI PMID
[39]	Nacry P, Bouguyon E, Gojon A (2013). Nitrogen acquisition by roots: physiological and developmental mechanisms ensuring plant adaptation to a fluctuating resource. Plant and Soil, 370, 1-29.
[40]	Näsholm T, Kielland K, Ganeteg U (2009). Uptake of organic nitrogen by plants. New Phytologist, 182, 31-48. DOI PMID
[41]	Nordin A, Högberg P, Näsholm T (2001). Soil nitrogen form and plant nitrogen uptake along a boreal forest productivity gradient. Oecologia, 129, 125-132. DOI PMID
[42]	Pinno BD, Wilson SD (2013). Fine root response to soil resource heterogeneity differs between grassland and forest. Plant Ecology, 214, 821-829.
[43]	Pregitzer KS, DeForest JL, Burton AJ, Allen MF, Ruess RW, Hendrick RL (2002). Fine root architecture of nine North American trees. Ecological Monographs, 72, 293-309.
[44]	Qin L, Walk TC, Han P, Chen L, Zhang S, Li Y, Hu X, Xie L, Yang Y, Liu J, Lu X, Yu C, Tian J, Shaff JE, Kochian LV, Liao X, Liao H (2019). Adaption of roots to nitrogen deficiency revealed by 3D quantification and proteomic analysis. Plant Physiology, 179, 329-347. DOI PMID
[45]	Rasmussen IS, Dresbøll DB, Thorup-Kristensen K (2015). Winter wheat cultivars and nitrogen (N) fertilization- Effects on root growth, N uptake efficiency and N use efficiency. European Journal of Agronomy, 68, 38-49.
[46]	Ren H, Gao GQ, Ma YY, Li ZW, Gu JC (2021). Root nitrogen uptake and its relationship with root morphological and chemical traits in Pinus koraiensis at different ages. Journal of Beijing Forestry University, 43(10), 65-72.
	[ 任浩, 高国强, 马耀远, 李祖旺, 谷加存 (2021). 不同年龄红松根系氮素吸收及其与根形态和化学性状的关系. 北京林业大学学报, 43(10), 65-72.]
[47]	Schimel JP, Bennett J (2004). Nitrogen mineralization: challenges of a changing paradigm. Ecology, 85, 591-602.
[48]	Simon J, Dannenmann M, Gasche R, Holst J, Mayer H, Papen H, Rennenberg H (2011). Competition for nitrogen between adult European beech and its offspring is reduced by avoidance strategy. Forest Ecology and Management, 262, 105-114.
[49]	Sun L, Chang X, Yu X, Jia G, Chen L, Liu Z, Zhu X (2019). Precipitation and soil water thresholds associated with drought-induced mortality of farmland shelter forests in a semi-arid area. Agriculture Ecosystems & Environment, 284, 106595. DOI: 10.1016/j.agee.2019.106595.
[50]	Templer PH, Dawson TE (2004). Nitrogen uptake by four tree species of the Catskill Mountains, New York:implications for forest N dynamics. Plant and Soil, 262, 251-261.
[51]	Tian H, Song HX, Wu XW, Zhang ZH (2022). The root elongation and the changes of cell wall components of rapeseed root under low nitrogen conditions. Journal of Hunan Agricultural University (Natural Sciences), 48, 386-393.
	[ 田辉, 宋海星, 吴秀文, 张振华 (2022). 低氮条件下油菜根系伸长与细胞壁组分的变化. 湖南农业大学学报(自然科学版), 48, 386-393.]
[52]	Wang X, Zhang C, Hasi E, Dong Z (2010). Has the Three-North Forest Shelterbelt Program solved the desertification and dust storm problems in arid and semiarid China? Journal of Arid Environments, 74, 13-22.
[53]	Xu X, Li Q, Wang J, Zhang L, Tian S, Zhi L, Li Q, Sun Y (2014). Inorganic and organic nitrogen acquisition by a fern Dicranopteris dichotoma in a subtropical forest in South China. PLoS ONE, 9, e90075. DOI: 10.1371/journal.pone.0090075.
[54]	Ye ZQ, Deng RJ, Wang YC, Wang JM, Li JW, Zhang FB, Chen J (2018). Branching patterns of clonal root of Populus euphratica and its associations with soil factors. Journal of Beijing Forestry University, 40(2), 31-39.
	[ 叶子奇, 邓如军, 王雨辰, 王健铭, 李景文, 张凡兵, 陈杰 (2018). 胡杨繁殖根系分枝特征及其与土壤因子的关联性. 北京林业大学学报, 40(2), 31-39.]
[55]	Yi R, Liu Q, Yang F, Dai X, Meng S, Fu X, Li S, Kou L, Wang H (2023). Complementary belowground strategies underlie species coexistence in an early successional forest. New Phytologist, 238, 612-623. DOI PMID
[56]	Zhang XX (2020). Analysis on restoration of degraded stand of three-north shelterbelt in Hebei Province. Protection Forest Science and Technology, (9), 77-78.
	[ 张昕欣 (2020). 河北省三北防护林退化林分修复浅析. 防护林科技, (9), 77-78.]
[57]	Zou TT, Zhang ZL, Li N, Yuan YS, Zheng DH, Liu Q, Yin HJ (2017). Differential uptakes of different forms of soil nitrogen among major tree species in subalpine coniferous forests of western Sichuan, China. Chinese Journal of Plant Ecology, 41, 1051-1059.
	[ 邹婷婷, 张子良, 李娜, 袁远爽, 郑东辉, 刘庆, 尹华军 (2017). 川西亚高山针叶林主要树种对土壤中不同形态氮素的吸收差异. 植物生态学报, 41, 1051-1059.] DOI

防护林 Shelterbelt	经纬度 Latitude and longitude	海拔 Altitude (m)	年龄 Age (a)	株高 Tree height (m)	基径 Basal diameter (cm)	防护林长度 Length of shelterbelt (m)	防护林宽度 Width of shelterbelt (m)	树间距 Spacing of trees (m)
小叶杨 Populus simonii	114.74° E, 42.02° N	1 445	29	8.10 ± 0.41	25.29 ± 2.16	1 000	10	2.5
榆树 Ulmus pumila	114.79° E, 42.12° N	1 312	36	6.94 ± 0.53	21.16 ± 1.96	1 800	25	2.5
宁夏枸杞 Lycium barbarum	114.74° E, 41.93° N	1 448	15	2.24 ± 0.16	4.17 ± 0.93	500	5	0.1
柠条锦鸡儿 Caragana korshinskii	114.80° E, 42.13° N	1 283	17	0.89 ± 0.13	1.30 ± 0.15	5 000	10	0.1

防护林 Shelterbelt	经纬度 Latitude and longitude	海拔 Altitude (m)	年龄 Age (a)	株高 Tree height (m)	基径 Basal diameter (cm)	防护林长度 Length of shelterbelt (m)	防护林宽度 Width of shelterbelt (m)	树间距 Spacing of trees (m)
小叶杨 Populus simonii	114.74° E, 42.02° N	1 445	29	8.10 ± 0.41	25.29 ± 2.16	1 000	10	2.5
榆树 Ulmus pumila	114.79° E, 42.12° N	1 312	36	6.94 ± 0.53	21.16 ± 1.96	1 800	25	2.5
宁夏枸杞 Lycium barbarum	114.74° E, 41.93° N	1 448	15	2.24 ± 0.16	4.17 ± 0.93	500	5	0.1
柠条锦鸡儿 Caragana korshinskii	114.80° E, 42.13° N	1 283	17	0.89 ± 0.13	1.30 ± 0.15	5 000	10	0.1

物种 Species	pH	含水量 Water content (%)	有机碳含量 Organic carbon content (g·kg^-1)	全氮含量 Total nitrogen content (g·kg^-1)	铵态氮含量 Ammonium nitrogen content (mg·kg^-1)	硝态氮含量 Nitrate nitrogen content (mg·kg^-1)	甘氨酸氮含量 Glycine nitrogen content (mg·kg^-1)
小叶杨 Populus simonii	8.31 ± 0.04^ab	14.18 ± 0.93^b	15.18 ± 0.79^ab	1.81 ± 0.24^ab	6.80 ± 0.52^a	20.84 ± 1.84^b	0.04 ± 0.01^a
榆树 Ulmus pumila	8.41 ± 0.09^a	16.72 ± 2.03^ab	14.46 ± 0.87^bc	1.50 ± 0.13^b	6.66 ± 0.65^a	34.21 ± 3.18^a	0.04 ± 0.01^a
宁夏枸杞 Lycium barbarum	8.07 ± 0.11^b	21.02 ± 0.93^a	18.06 ± 1.27^a	2.23 ± 0.18^a	6.56 ± 0.28^a	39.99 ± 3.13^a	0.03 ± 0.00^ab
柠条锦鸡儿 Caragana korshinskii	8.49 ± 0.01^a	16.98 ± 0.62^ab	11.55 ± 0.50^c	1.61 ± 0.12^b	6.41 ± 0.24^a	11.59 ± 1.31^c	0.02 ± 0.00^b

物种 Species	pH	含水量 Water content (%)	有机碳含量 Organic carbon content (g·kg^-1)	全氮含量 Total nitrogen content (g·kg^-1)	铵态氮含量 Ammonium nitrogen content (mg·kg^-1)	硝态氮含量 Nitrate nitrogen content (mg·kg^-1)	甘氨酸氮含量 Glycine nitrogen content (mg·kg^-1)
小叶杨 Populus simonii	8.31 ± 0.04^ab	14.18 ± 0.93^b	15.18 ± 0.79^ab	1.81 ± 0.24^ab	6.80 ± 0.52^a	20.84 ± 1.84^b	0.04 ± 0.01^a
榆树 Ulmus pumila	8.41 ± 0.09^a	16.72 ± 2.03^ab	14.46 ± 0.87^bc	1.50 ± 0.13^b	6.66 ± 0.65^a	34.21 ± 3.18^a	0.04 ± 0.01^a
宁夏枸杞 Lycium barbarum	8.07 ± 0.11^b	21.02 ± 0.93^a	18.06 ± 1.27^a	2.23 ± 0.18^a	6.56 ± 0.28^a	39.99 ± 3.13^a	0.03 ± 0.00^ab
柠条锦鸡儿 Caragana korshinskii	8.49 ± 0.01^a	16.98 ± 0.62^ab	11.55 ± 0.50^c	1.61 ± 0.12^b	6.41 ± 0.24^a	11.59 ± 1.31^c	0.02 ± 0.00^b

指标 Factor		缩写 Abbreviation	氮吸收速率 Nitrogen uptake rate (µg·g^-1·h^-1)
指标 Factor		缩写 Abbreviation	铵态氮 Ammonium nitrogen	硝态氮 Nitrate nitrogen	甘氨酸氮 Glycine nitrogen	总氮 Total nitrogen
根性状 Root trait	根直径 Root diameter (mm)	AD	-0.021	-0.688^**	-0.108	0.003
	根组织密度 Root tissue density (g·cm^-2)	RTD	0.264	-0.637^**	0.099	0.290
	比根长 Specific root length (m·g^-1)	SRL	-0.287	0.694^**	-0.094	-0.309
	比表面积 Specific surface area (cm²·g^-1)	SSA	-0.324	0.714^**	-0.100	-0.335
	分支比 Branching ratio	BR	-0.358	-0.218	-0.176	-0.235
	分支强度 Branching intensity (cm^-1)	BI	0.403	0.175	0.638^**	0.512^*
	根碳含量 Root carbon content (%)	RC	-0.592^*	0.053	-0.594^*	-0.662^**
	根氮含量 Root nitrogen content (%)	RN	-0.816^**	0.061	-0.685^**	-0.758^*
	根碳氮比 Ratio of carbon to nitrogen	C:N	0.823^*	-0.109	0.700^**	0.765^**
土壤 Soil	土壤pH Soil pH	pH	0.137	-0.492	0.225	0.308
	土壤含水量 Soil water content (%)	SWC	-0.686^**	0.346	-0.500^*	-0.571^*
	土壤有机碳含量 Soil organic carbon content (g·kg^-1)	SC	-0.072	0.613^*	-0.079	-0.115
	土壤全氮含量 Soil total nitrogen content (g·kg^-1)	SN	-0.442	0.584^*	-0.443	-0.462
	土壤铵态氮含量 Soil ammonium nitogen content (mg·kg^-1)	SAM	-0.035	0.448	0.015	0.082
	土壤硝态氮含量 Soil nitrate nitogen content (mg·kg^-1)	SNT	-0.275	0.750^**	0.088	-0.156
	土壤甘氨酸氮含量 Soil glycine nitogen content (mg·kg^-1)	SGLY	0.564^*	0.290	0.490	0.507^*