不同氮磷比处理对甘草生长与生态化学计量特征的影响

doi:10.17521/cjpe.2016.0230

摘要/Abstract

摘要：

大气氮(N)沉降增加加速了生态系统N循环, 导致生态系统磷(P)需求增加。开展不同N:P处理对荒漠草原植物生长和生态化学计量特征影响的研究, 不仅可为预测长期大气N沉降增加条件下植物和土壤的相互作用提供新思路, 而且可为全球变化背景下我国北方草地植被的可持续管理提供科学指导。该文通过2013-2014年针对甘草(Glycyrrhiza uralensis)设立的不同N:P的盆栽控制试验, 研究了不同N:P处理对甘草生物量和碳(C)、N、P化学计量学特征(叶片、根系和土壤)的影响, 比较了C:N:P化学计量学特征在叶片、根系和土壤3个库间的差异和联系, 探讨了土壤C:N:P化学计量比对甘草生长和养分摄取的指示作用。结果显示: N:P的适当减小降低了土壤和甘草(叶片和根系)的C:P和N:P, 提高了甘草地上和地下生物量, 说明适量的P添加提高了土壤P有效性和甘草P摄取能力、促进了甘草生长和生物量积累。但过低的N:P处理(高P添加)使土壤C:P和N:P显著下降, 抑制了甘草对N的摄取, 从而不利于甘草生长; 甘草叶片和根系(尤其叶片) C:N:P化学计量学特征均与土壤C:N:P化学计量学特征存在不同程度的相关性, 意味着土壤C、N、P及其计量关系的改变会直接作用于植物。以上结果表明, 适当的人为P添加可通过调节土壤和植物叶片C:N:P化学计量学特征, 缓解土壤和植物间P的供需压力, 从而减缓长期大气N沉降增加对荒漠草原群落结构的不利影响。

关键词: 生态化学计量特征, 荒漠草原, 甘草, 磷添加

Abstract:

Aims The increase in atmospheric nitrogen (N) deposition has accelerated N cycling of ecosystems, probably resulting in increases in phosphorus (P) demand of ecosystems. Studies on the effects of artificial N:P treatment on the growth and carbon (C), N, P ecological stoichiometry of desert steppe species could provide not only a new insight into the forecasting of how the interaction between soils and plants responses to long-term atmospheric N deposition increase, but also a scientific guidance for sustainable management of grassland in northern China under global climate change. Methods Based on a pot-cultured experiment conducted for Glycyrrhiza uralensis (an N-fixing species) during 2013 to 2014, we studied the effects of different N:P supply ratios (all pots were treated with the same amount of N but with different amounts of P) on aboveground biomass, root biomass, root/shoot ratio, and C:N:P ecological stoichiometry both in G. uralensis (leaves and roots) and in soils. Additionally, through the correlation analyses between biomass and C:N:P ecological stoichiometry in leaves, roots, and soils, we compared the differences among the C:N:P ecological stoichiometry of the three pools, and discussed the indication of C:N:P ecological stoichiometry in soils for the growth and nutrient uptake of G. uralensis. Important findings The results showed that, reducing N:P decreased C:P and N:P ratios both in G. uralensis (leaves and roots) and in soils but increased aboveground biomass and root biomass of G. uralensis, indicating that low to moderate P addition increased P availability of soils and P uptake of G. uralensis. However, excessive low N:P (high P addition) led to great decreases in soil C:P and N:P ratios, thus hindering N uptake and the growth of G. uralensis. C:N:P ratios in the two pools of G. uralensis (especially in leaves) had close correlations with soil C:N:P ratio, indicating that the change in soil C:N:P ratio would have a direct influence on plants. Our results suggest that, through regulating C:N:P ratio in leaves and soils, appropriate amounts of P addition could balance soil P supply and plant P demand and compensate the opposite influences of long-term atmospheric N deposition increase on the structure of desert steppe.

Key words: ecological stoichiometry, desert steppe, Glycyrrhiza uralensis, phosphorus addition

黄菊莹, 余海龙, 王丽丽, 马凯博, 康扬眉, 杜雅仙. 不同氮磷比处理对甘草生长与生态化学计量特征的影响. 植物生态学报, 2017, 41(3): 325-336. DOI: 10.17521/cjpe.2016.0230

Ju-Ying HUANG, Hai-Long YU, Li-Li WANG, Kai-Bo MA, Yang-Mei KANG, Ya-Xian DU. Effects of different nitrogen:phosphorus levels on the growth and ecological stoichiometry of Glycyrrhiza uralensis. Chinese Journal of Plant Ecology, 2017, 41(3): 325-336. DOI: 10.17521/cjpe.2016.0230

导出引用管理器 EndNote|Ris|BibTeX

链接本文: https://www.plant-ecology.com/CN/10.17521/cjpe.2016.0230

https://www.plant-ecology.com/CN/Y2017/V41/I3/325

图/表 8

表1 甘草移栽前土壤本底值

Table 1 Basic soil properties before Glycyrrhiza uralensis transplanting

土壤有机碳 Soil organic carbon (g·kg^-1)	土壤全氮 Soil total nitrogen (g·kg^-1)	土壤全磷 Soil total phosphorus (g·kg^-1)	NH₄⁺-N (mg·kg^-1)	NO₃^--N (mg·kg^-1)	土壤速效磷 Soil available phosphorus (mg·kg^-1)
1.8	0.2	0.3	1.2	8.3	13.8

图1 不同氮(N)磷(P)比处理对甘草生物量和根冠比的影响(平均值±标准误差, n = 5)。N10P1、N10P2、N10P4、N10P8、N10P16和N10P32代表在统一施用10.0 g·m-2·a-1 N的基础上,分别施入1.0、2.0、4.0、8.0、16.0和32.0 g·m-2·a-1的P。不同小写字母表示N:P处理间指标差异显著(p < 0.05), 相同字母表示差异不显著(p > 0.05)。

Fig. 1 Effects of nitrogen (N):phosphorus (P) level on root and aboveground biomass and root/shoot ratio of Glycyrrhiza uralensis (mean ± SE, n = 5). N10P1, N10P2, N10P4, N10P8, N10P16, and N10P32 represent all pots treated with 10.0 g·m-2·a-1 amount of N but with different amounts of P: 1.0, 2.0, 4.0, 8.0, 16.0, and 32.0 g·m-2·a-1, respectively. Different lowercase letters indicate significant difference (p < 0.05) between indices within N:P levels. The same lowercase letters indicate insignificant differences (p > 0.05).

图2 不同氮(N)磷(P)比处理对甘草叶片碳(C)、N、P及其化学计量比的影响(平均值±标准误差, n = 5)。N10P1、N10P2、N10P4、N10P8、N10P16和N10P32代表在统一施用10.0 g·m-2·a-1 N的基础上, 分别施入1.0、2.0、4.0、8.0、16.0和32.0 g·m-2·a-1的P。不同小写字母表示N:P处理间指标差异显著(p < 0.05), 相同字母表示差异不显著(p > 0.05)。

Fig. 2 Effects of nitrogen (N):phosphorus (P) level on leaf carbon (C), N, P and their stoichiometry ratios of Glycyrrhiza uralensis (mean ± SE, n = 5). N10P1, N10P2, N10P4, N10P8, N10P16, and N10P32 represent all pots treated with 10.0 g·m-2·a-1 amount of N but with different amounts of P: 1.0, 2.0, 4.0, 8.0, 16.0, and 32.0 g·m-2·a-1, respectively. Different lowercase letters indicate significant difference (p < 0.05) between indices within N:P levels. The same lowercase letters indicate insignificant difference (p > 0.05).

图3 不同氮(N)磷(P)比处理对甘草根系碳(C)、N、P及其化学计量比的影响(平均值±标准误差, n = 5)。N10P1、N10P2、N10P4、N10P8、N10P16和N10P32代表在统一施用10.0 g·m-2·a-1 N的基础上, 分别施入1.0、2.0、4.0、8.0、16.0和32.0 g·m-2·a-1的P。不同小写字母表示N:P处理间指标差异显著(p < 0.05), 相同字母表示差异不显著(p > 0.05)。

Fig. 3 Effects of nitrogen (N): phosphorus (P) level on root carbon (C), N, P and their stoichiometry ratios of Glycyrrhiza uralensis (mean ± SE, n = 5). N10P1, N10P2, N10P4, N10P8, N10P16, and N10P32 represent all pots were treated with 10.0 g·m-2·a-1 amount of N but with differing amounts of P: 1.0, 2.0, 4.0, 8.0, 16.0, and 32.0 g·m-2·a-1, respectively. Different lowercase letters indicate significant differences (p < 0.05) between indices within N:P levels. The same lowercase letters indicate insignificant differences (p > 0.05).

图4 不同氮(N)磷(P)比处理对土壤碳(C)、N、P含量的影响(平均值±标准误差, n = 5)。N10P1、N10P2、N10P4、N10P8、N10P16和N10P32代表在统一施用10.0 g·m-2·a-1 N的基础上, 分别施入1.0、2.0、4.0、8.0、16.0和32.0 g·m-2·a-1的P。不同小写字母表示N:P处理间指标差异显著(p < 0.05), 相同字母表示差异不显著(p > 0.05)。

Fig. 4 Effects of nitrogen (N):phosphorus (P) level on soil carbon (C), N, and P content (mean ± SE, n = 5). N10P1, N10P2, N10P4, N10P8, N10P16, and N10P32 represent all pots treated with 10.0 g·m-2·a-1 amount of N but with different amounts of P: 1.0, 2.0, 4.0, 8.0, 16.0, and 32.0 g·m-2·a-1, respectively. Different lowercase letters indicate significant difference (p < 0.05) between indices within N:P levels. The same lowercase letters indicate insignificant difference (p > 0.05).

表2 甘草与土壤碳(C)、氮(N)、磷(P)含量及其化学计量比间的相关系数

Table 2 Correlation coefficients between carbon (C), nitrogen (N), phosphorus (P ) and their stoichiometry ratios in Glycyrrhiza uralensis and in soils

指标 Index	土壤有机C Soil organic C (g·kg^-1)	土壤全N Soil total N (g·kg^-1)	土壤全P Soil total P (g·kg^-1)	土壤速效P Soil available P (mg·kg^-1)	土壤C:N C_soil:N_soil	土壤C:P C_soil:P_soil	土壤N:P N_soil:P_soil
地上生物量 Aboveground biomass (g·plant^-1)	ns	ns	ns	0.51^*	ns	ns	0.05
地下生物量 Belowground biomass (g·plant^-1)	ns	ns	ns	ns	0.50^*	ns	ns
叶片全C Leaf total C (mg·g^-1)	ns	ns	ns	ns	ns	ns	ns
叶片全N Leaf total N (mg·g^-1)	ns	-0.56^*	ns	ns	0.69^**	0.50^*	ns
叶片全P Leaf total P (mg·g^-1)	ns	ns	0.77^**	ns	ns	-0.70^**	-0.75^**
叶片C:N C_leaf:N_leaf	ns	ns	ns	ns	-0.56^*	ns	ns
叶片C:P C_leaf:P_leaf	ns	ns	-0.63^**	ns	ns	0.58^*	0.64^**
叶片N:P N_leaf:P_leaf	ns	ns	-0.80^**	-0.49^*	0.57^*	0.85^**	0.79^**
根系全C Root total C (mg·g^-1)	ns	ns	ns	0.62^**	ns	ns	-0.53^*
根系全N Root total N (mg·g^-1)	ns	ns	-0.50^*	ns	ns	ns	ns
根系全P Root total P (mg·g^-1)	ns	ns	ns	ns	ns	ns	ns
根系C:N C_root:N_root	ns	ns	0.66^**	ns	ns	-0.58^*	-0.70^**
根系C:P C_root:P_root	ns	ns	ns	ns	ns	ns	ns
根系N:P N_root:P_root	ns	ns	-0.57^*	ns	ns	0.65^**	0.67^**

表3 碳(C):氮(N):磷(P)化学计量学特征与甘草生物量和根冠比的相关系数

Table 3 Correlation coefficients between carbon (C):nitrogen (N):phosphorus (P) ecological stoichiometry and the biomass or root/shoot ratio of Glycyrrhiza uralensis

指标 Index	地上生物量 Aboveground biomass (g·plant^-1)	地下生物量 Belowground biomass (g·plant^-1)	总生物量 Total biomass (g·plant^-1)	根冠比 Root/shoot ratio
土壤有机C Soil organic C (g·kg^-1)	0.18	0.35	0.32	-0.37
土壤全N Soil total N (g·kg^-1)	-0.01	-0.33	-0.23	-0.21
土壤全P Soil total P (g·kg^-1)	-0.27	-0.39	-0.39	0.01
土壤速效P Soil available P (mg·kg^-1)	0.51^*	0.18	0.35	-0.05
土壤C:N C_soil:N_soil	0.12	0.50^*	0.40	0.04
土壤C:P C_soil:P_soil	-0.00	0.19	0.13	0.18
土壤N:P N_soil:P_soil	0.05	0.07	0.07	0.13
叶片全C Leaf total C (mg·g^-1)	0.07	-0.08	-0.03	-0.33
叶片全N Leaf total N (mg·g^-1)	0.25	0.35	0.35	-0.27
叶片全P Leaf total P (mg·g^-1)	-0.07	-0.31	-0.25	-0.25
叶片C:N C_leaf:N_leaf	-0.18	-0.21	-0.22	0.27
叶片C:P C_leaf:P_leaf	0.02	0.22	0.16	0.41
叶片N:P N_leaf:P_leaf	0.07	0.29	0.23	0.15
根系全C Root total C (mg·g^-1)	0.39	0.39	0.44	-0.68
根系全N Root total N (mg·g^-1)	0.49^*	0.21	0.36	-0.58
根系全P Root total P (mg·g^-1)	0.43	0.19	0.32	-0.55
根系C:N C_root:N_root	-0.22	-0.03	-0.12	0.10
根系C:P C_root:P_root	-0.29	-0.05	-0.17	0.39
根系N:P N_root:P_root	-0.07	-0.04	-0.06	0.18

图5 不同氮(N)磷(P)比处理对土壤碳(C):N:P化学计量比的影响(平均值±标准误差, n = 5)。N10P1、N10P2、N10P4、N10P8、N10P16和N10P32代表在统一施用10.0 g·m-2·a-1 N的基础上, 分别施入1.0、2.0、4.0、8.0、16.0和32.0 g·m-2·a-1的P。不同小写字母表示N:P处理间指标差异显著(p < 0.05), 相同字母表示差异不显著(p > 0.05)。

Fig. 5 Effects of nitrogen (N): phosphorus (P) level on soil carbon (C) :N:P stoichiometry ratio (mean ± SE, n = 5). N10P1, N10P2, N10P4, N10P8, N10P16, and N10P32 represent all pots treated with 10.0 g·m-2·a-1 amount of N but with different amounts of P: 1.0, 2.0, 4.0, 8.0, 16.0, and 32.0 g·m-2·a-1, respectively. Different lowercase letters indicate significant difference (p < 0.05) between indices within N:P levels. The same lowercase letters indicate insignificant difference (p > 0.05).

参考文献 37

[1]	Bao SD (2000). Soil and Agricultural Chemistry Analysis. 3rd ed. China Agriculture Press, Beijing. (in Chinese).[鲍士旦 (2000). 土壤农化分析. 第三版. 中国农业出版社, 北京.]
[2]	Bobbink R, Hicks K, Galloway J, Spranger T, Alkemade R, Ashmore M, Bustamante M, Cinderby S, Davidson E, Dentener F, Emmett B, Erisman JW, Fenn M, Gilliam F, Nordin A, Pardo L, de Vries W (2010). Global assessment of nitrogen deposition effects on terrestrial plant diversity: A synthesis. Ecological Applications, 20, 30-59.
[3]	Chen FS, Hu XF, Ge G (2007). Leaf N:P stoichiometry and nutrient resorption efficiency of Ophiopogon japonicus in Nanchang City. Acta Prataculturae Sinica, 16(4), 47-54. (in Chinese with English abstract)[陈伏生, 胡小飞, 葛刚 (2007). 城市地被植物麦冬叶片氮磷和养分再吸收效率. 草业学报, 16(4), 47-54.]
[4]	Clark CM, Tilman D (2008). Loss of plant species after chronic low-level nitrogen deposition to prairie grasslands. Nature, 451, 712-715.
[5]	Cleveland CC, Liptzin D (2007). C:N:P stoichiometry in soil: Is there a “Redfield ratio” for the microbial biomass? Biogeochemistry, 85, 235-252.
[6]	Crews TE, Farrington H, Vitousek PM (2000). Changes in a symbiotic, heterotrophic nitrogen fixation on leaf litter of Metrosideros polymorpha with long-term ecosystem development in Hawaii. Ecosystems, 3, 386-395.
[7]	Cross AF, Schlesinger WH (2001). Biological and geochemical controls on phosphorus fractions in semiarid soils. Biogeochemistry, 52, 155-172.
[8]	Crous JW, Morris AR, Scholes MC (2008). Growth and foliar nutrient response to recent applications of phosphorus (P) and potassium (K) and to residual P and K fertiliser applied to the previous rotation of Pinus patula at Usutu, Swaziland. Forest Ecology Management, 256, 712-721.
[9]	Delgado-Baquerizo M, Maestre FT, Gallardol A, Bowker MA, Wallenstein MD, Quero JL, Ochoa V, Gozalo B, García- Gómez M, Soliveres S, García-Palacios P, Berdugo M, Valencia E, Escolar C, Arredondo T, Barraza-Zepeda C, Bran D, Carreira JA, Chaieb M, Conceicão AA, Derak M, Eldridge DJ, Escudero A, Espinosa CI, Gaitán J, Gatica MG, Gómez-González S, Guzman E, Gutiérrez JR, Florentino A, Hepper E, Hernández RM, Huber-Sannwald E, Jankju M, Liu J, Mau RL, Miriti M, Monerris J, Naseri K, Noumi Z, Polo V, Prina A, Pucheta E, Ramírez E, Ramírez-Collantes DA, Romão R, Tighe M, Torres D, Torres-Díaz C, Ungar ED, Val J, Wamiti W, Wang D, Zaady E (2013). Decoupling of soil nutrient cycles as a function of aridity in global drylands. Nature, 502, 672-676.
[10]	Duan L, Hao JM, Xie SD, Zhou ZP (2002). Estimating critical loads of sulfur and nitrogen for Chinese soils by steady state method. Journal of Environmental Science, 23(2), 7-12. (in Chinese with English abstract).[段雷, 郝吉明, 谢绍东, 周中平 (2002). 用稳态法确定中国土壤的硫沉降和氮沉降临界负荷. 环境科学, 23(2), 7-12.]
[11]	Fritz C, van Dijk G, Smolders AJP, Pancotto VA, Elzenga TJTM, Roelofs JGM, Grootjans AP (2012). Nutrient additions in pristine Patagonian Sphagnum bog vegetation: Can phosphorus addition alleviate (the effects of) increased nitrogen loads. Plant Biology, 14, 491-499.
[12]	Guo ZW, Chen SL, Yang QP, Li YC (2012). Responses of N and P stoichiometry on mulching management in the stand of Phyllostachys praecox. Acta Ecologica Sinica, 32, 6361-6368. (in Chinese with English abstract)[郭子武, 陈双林, 杨清平, 李迎春 (2012). 雷竹林土壤和叶片N、P化学计量特征对林地覆盖的响应. 生态学报, 32, 6361-6368.]
[13]	Güsewell S (2005). Responses of wetland graminoids to the relative supply of nitrogen and phosphorus. Plant Ecology, 176, 35-55.
[14]	He LY, Hu ZM, Guo Q, Li SG, Bai WM, Li LH (2015). Influence of nitrogen and phosphorus addition on the aboveground biomass in Inner Mongolia temperate steppe, China. Chinese Journal of Applied Ecology, 26, 2291-2297. (in Chinese with English abstract)[何利元, 胡中民, 郭群, 李胜功, 白文明, 李凌浩 (2015). 氮磷添加对内蒙古温带草地地上生物量的影响. 应用生态学报, 26, 2291-2297.]
[15]	Huang JY, Yu HL (2016). Responses of growth of four desert species to different N addition levels. Chinese Journal of Plant Ecology, 40, 165-176. (in Chinese with English abstract)[黄菊莹, 余海龙 (2016). 4个荒漠草原物种的生长对不同氮添加水平的响应. 植物生态学报, 40, 165-176.]
[16]	Huang JY, Yu HL, Lin H, Zhang Y, Searle EB, Yuan ZY (2016). Phosphorus amendment mitigates nitrogen addition-induced phosphorus limitation in two plant species in a desert steppe, China. Plant and Soil, 399, 221-232.
[17]	IPCC (Intergovernmental Panel on Climate Change) (2013). Climate Change 2013: The Physical Science Basis. Cambridge University Press, Cambridge, UK.
[18]	Jones AG, Power SA (2012). Field-scale evaluation of effects of nitrogen deposition on the functioning of heathland ecosystems. Journal of Ecology, 100, 331-342.
[19]	Li XB, Chen L, LI GQ, An H (2013). Influence of enclosure on Glyeyrrhiza uralensis community and distribution pattern in arid and semi-arid areas. Acta Ecologica Sinica, 33, 3995-4001. (in Chinese with English abstract)[李学斌, 陈林, 李国旗, 安慧 (2013). 干旱半干旱地区围栏封育对甘草群落特征及其分布格局的影响. 生态学报, 33, 3995-4001.]
[20]	Li XB, Zhao ZF, Chen L, An H, Li GQ, Liu BR (2012). The status and countermeasures of development on licorices industry of Ningxia. Ecological Economy, 12, 132-135. (in Chinese with English abstract)[李学斌, 赵志锋, 陈林, 安慧, 李国旗, 刘秉儒 (2012). 宁夏甘草产业发展现状及对策研究. 生态经济, 12, 132-135.]
[21]	Liu C, Wang Y, Wang N, Wang GX (2012). Advances research in plant nitrogen, phosphorus and their stoichiometry in terrestrial ecosystems: A review. Chinese Journal of Plant Ecology, 36, 1205-1216. (in Chinese with English abstract)[刘超, 王洋, 王楠, 王根轩 (2012). 陆地生态系统植被氮磷化学计量研究进展. 植物生态学报, 36, 1205-1216.]
[22]	Liu P, Huang JH, Sun OJX (2010). Litter decomposition and nutrient release as affected by soil nitrogen availability and litter quality in a semiarid grassland ecosystem. Oecologia, 162, 771-780.
[23]	Liu XJ, Zhang Y, Han WX, Tang AH, Shen JL, Cui ZL, Vitousek P, Erisman JW, Goulding K, Christie P, Fangmeier A, Zhang FS (2013). Enhanced nitrogen deposition over China. Nature, 494, 459-462.
[24]	Liu Y, Zhang J, Chen YM, Chen L, Liu Q (2013). Effect of nitrogen and phosphorus fertilization on biomass allocation and C:N:P stoichiometric characteristics of Eucalyptus grandis seedlings. Chinese Journal of Plant Ecology, 37, 933-941. (in Chinese with English abstract)[刘洋, 张健, 陈亚梅, 陈磊, 刘强 (2013). 氮磷添加对巨桉幼苗生物量分配和C:N:P化学计量特征的影响. 植物生态学报, 37, 933-941.]
[25]	Mayor JR, Wright SJ, Turner BL (2014). Species-specific responses of foliar nutrients to long-term nitrogen and phosphorus additions in a lowland tropical forest. Journal of Ecology, 102, 36-44.
[26]	Naples BK, Fisk MC (2010). Belowground insights into nutrient limitation in northern hardwood forests. Biogeochemistry, 97, 109-121.
[27]	Phoenix GK, Booth RE, Leake JR, Read DJ, Grime JP, Lee JA (2004). Simulated pollutant nitrogen deposition increases P demand and enhances root-surface phosphatase activities of three plant functional types in a calcareous grassland. New Phytologist, 161, 279-289.
[28]	Phuyal M, Artz RRE, Sheppard L, Leith ID, Johnson D (2008). Long-term nitrogen deposition increases phosphorus limitation of bryophytes in an Ombrotrophic Bog. Plant Ecology, 196, 111-121.
[29]	Shi XM, Qi JH, Song L, Liu WY, Huang JB, Li S, Lu HZ, Chen X (2015). C, N and P stoichiometry of two dominant seedlings and their responses to nitrogen additions in the montane moist evergreen broad-leaved forest in Ailao Mountains, Yunnan. Chinese Journal of Plant Ecology, 39, 962-970. (in Chinese with English abstract)[石贤萌, 杞金华, 宋亮, 刘文耀, 黄俊彪, 李苏, 卢华正, 陈曦 (2015). 哀牢山中山湿性常绿阔叶林两种优势幼苗C、N、P化学计量特征及其对N沉降增加的响应. 植物生态学报, 39, 962-970.]
[30]	Tian HQ, Chen GS, Zhang C, Melillo JM, Hall CAS (2010). Pattern and variation of C:N:P ratios in China’s soils: A synthesis of observational data. Biogeochemistry, 98, 139-151.
[31]	Wardle DA, Gundale MJ, Jaderlund A, Nilsson MC (2013). Decoupled long-term effects of nutrient enrichment on aboveground and belowground properties in subalpine tundra. Ecology, 94, 904-919.
[32]	Yang XX, Ren F, Zhou HK, He JS (2014). Responses of plant community biomass to nitrogen and phosphorus additions in an alpine meadow on the Qinghai-Xizang Plateau. Chinese Journal of Plant Ecology, 38, 159-166. (in Chinese with English abstract)[杨晓霞, 任飞, 周华坤, 贺金生 (2014). 青藏高原高寒草甸植物群落生物量对氮、磷添加的响应. 植物生态学报, 38, 159-166.]
[33]	Yang YH, Fang JY, Ji CJ, Datta A, Li P, Ma WH, Mohammat A, Shen HH, Hu HF, Knapp BO, Smith P (2014). Stoichiometric shifts in surface soils over broad geographical scales: Evidence from China’s grasslands. Global Ecology and Biogeography, 23, 947-955.
[34]	Yu Q, Wu HH, He NP, Lü XT, Wang ZP, Elser JJ, Wu JG, Han XG (2012). Testing the growth-rate hypothesis in vascular plants with above- and below-ground biomass. PLOS ONE, 7, e32162. doi: 10.1371/journal.pone.0032162.
[35]	Yuan ZY, Chen HYH (2015). Decoupling of nitrogen and phosphorus in terrestrial plants associated with global changes. Nature Climate Change, 5, 465-469.
[36]	Zhao YF, Xu FL, Wang WL, Wang LL, Wang GX, Sun PY, Bai XF (2014). Seasonal variation in contents of C, N and P and stoichiometry characteristics in fine roots, stems and needles of Larix principis-rupprechtii. Chinese Bulletin of Botany, 49, 560-568. (in Chinese with English abstract)[赵亚芳, 徐福利, 王渭玲, 王玲玲, 王国兴, 孙鹏跃, 白小芳 (2014). 华北落叶松根茎叶碳氮磷含量及其化学计量学特征的季节变化. 植物学报, 49 , 560-568.]
[37]	Zhu FF, Yoh M, Gilliam FS, Lu XK, Mo JM (2013). Nutrient limitation in three lowland tropical forests in southern China receiving high nitrogen deposition: Insights from fine root responses to nutrient additions. PLOS ONE, 8, e82661. doi:10.1371/journal.pone.0082661.