Effects of nitrogen and water addition on soil respiration in a Nei Mongol desert steppe with different intensities of grazing history

doi:10.17521/cjpe.2018.0177

Abstract

Abstract:

Aims Soil respiration is an important indicator for evaluation of ecosystem health in the grazing grasslands of arid regions, and thus can be used to assess dynamics of ecosystem functioning during the restoration of degraded grasslands from enduring intensive grazing.
Methods This study was carried out in a Nei Mongol desert grassland with four grazing intensity treatments, i.e., control, light, moderate, and heavy grazing intensity designated as CK, LG, MG, and HG, respectively. Our objectives of this study were to explore the responses of soil respiration in these treatments with additional nitrogen (N) and water (W) addition. The plant community was dominated by a grass species, Stipa breviflora.
Important findings Our results showed that: (1) previous grazing intensity had significant impacts on soil respiration in 2016 and 2017, but not in 2015. Grazing increased soil respiration. Moreover, both nitrogen and water addition significantly enhanced soil respiration in MG plots, while only combined addition of nitrogen and water significantly increased soil respiration in HG plots. (2) Neither grazing intensity nor addition of nitrogen and water changed the seasonal dynamics of growing season soil respiration in this desert grassland. Soil respiration showed a single-peak curve model, and the peak occurred in July with both rain and heat. (3) The effects of nitrogen and water addition varied in different growing seasons. Nitrogen addition had no significant effects in the first two years (2015 and 2016), while showed significant effects in the third year (2017). Water addition had significant effects in years with normal precipitation (2015 and 2017), while had insignificant effect in the year with high precipitation (2016). Combined addition of nitrogen and water showed stronger effects than only addition of water in CK, LG, and HG plots, indicating that the synergistic effects of nitrogen and water addition on soil respiration. (4) The sensitivity of soil respiration to soil temperature at 10 cm depth (i.e., the Q₁₀ value) ranged between 1.13 and 2.41, with an average value of 1.71. Without addition of nitrogen and water, Q₁₀ values in grazing plots were all lower than in CK plots, with the lowest value occurring in HG plots. With the addition of water and combined addition of water and nitrogen, the Q₁₀ value increased significantly by 100%. Taken together, our results indicated that soil moisture was the leading environmental factor affecting soil respiration in this desert grassland, while nitrogen played an effective role only after the minimum requirement of water availability was met. Results from this study will provide important helpful information for the restoration and rational utilization of the degraded desert steppe.

Key words: desert steppe, grazing intensity, soil respiration, precipitation increase, nitrogen addition

WEN Chao,SHAN Yu-Mei,YE Ru-Han,ZHANG Pu-Jin,MU Lan,CHANG Hong,REN Ting-Ting,CHEN Shi-Ping,BAI Yong-Fei,HUANG Jian-Hui,SUN Hai-Lian. Effects of nitrogen and water addition on soil respiration in a Nei Mongol desert steppe with different intensities of grazing history[J]. Chin J Plant Ecol, 2020, 44(1): 80-92.

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https://www.plant-ecology.com/EN/Y2020/V44/I1/80

Figures/Tables 8

Fig. 1 Monthly mean air temperature and precipitation during the growing seasons across the study period 2015 to 2017, in Siziwang Banner.

Table 1 Results (F-value) of four-way ANOVA on the effects of month (M), grazing intensity (GI), water (W), nitrogen addition (N) and their interactions on growing season soil temperature (ST), soil moisture (SM) and soil respiration (SR), 2015 to 2017, in a Nei Mongol desert steppe

年份 Year	处理 Treatment	土壤温度 ST	土壤含水量 SM	土壤呼吸速率 SR
2015	M	90.56^***	160.57^***	120.88^***
	W	1.40	172.25^***	59.31^***
	M ′ W	0.38	9.10^***	3.27^*
2016	M	37.56^***	377.57^***	939.39^***
	GI	1.65	0.24	7.00^***
	W	0.32	404.03^***	75.63^***
	M ′ W	0.10	4.20^**	4.66^**
2017	M	30.82^***	103.92^***	79.29^***
	GI	1.42	0.49	4.26^**
	W	0.04	159.55^***	250.15^***
	N	0.33	10.92^**	41.55^***
	M ′ W	0.92	4.55^**	16.68^***
	W′ N	0.80	3.05	7.95^**

Fig. 2 Changes in growing season soil moisture content and soil temperature, 2015 to 2017, in a Nei Mongol desert steppe (mean + SE). CKs, N, W, NW represent no addition of water and nitrogen, addition of nitrogen, addition of water, and combined addition of water and nitrogen, respectively. Different lowercase letters indicate significant difference between treatments in the same year at the 0.05 level; different uppercase letters indicate a significant difference between years at the 0.05 level.

Fig. 3 Average soil respiration rate for 3 years under different grazing intensities under different treatments in a Nei Mongol desert steppe (mean + SE). CK, LG, MG, HG represent non-grazing, light grazing, moderate grazing and heavy grazing, respectively. CKs, N, W, NW represent no addition of water and nitrogen, addition of nitrogen, addition of water, and combined addition of water and nitrogen, respectively. Different lowercase letters indicate significant difference between treatments in the same year at the 0.05 level.

Fig. 4 Response of soil respiration to nitrogen and water addition in a Nei Mongol desert steppe (mean ± SE). CK, LG, MG, HG represent non-grazing, light grazing, moderate grazing and heavy grazing, respectively. CKs, N, W, NW represent no addition of water and nitrogen, addition of nitrogen, addition of water, and combined addition of water and nitrogen, respectively. *, p < 0.05; ns, p > 0.05。

Fig. 5 Effects of different grazing intensities on the average soil respiration rate during the three years (2015-2017) under different water and nitrogen treatments in a Nei Mongol desert steppe (mean + SE). CK, LG, MG, HG represent non-grazing, light grazing, moderate grazing and heavy grazing, respectively. CKs, N, W, NW represent no addition of water and nitrogen, addition of nitrogen, addition of water, and combined addition of water and nitrogen, respectively. Different lowercase letters indicate significant difference between treatments in the same year at the 0.05 level.

Table 2 Relationship between soil respiration rate and soil temperature at 10 cm depth in a Nei Mongol desert steppe

放牧强度 Grazing intensity	处理 Treatment	n	方程 Equation	R²	Q₁₀	p
CK	CKs	24	R_s = 0.35e^0.036^t	0.026	1.43	0.477
	N	24	R_s = 0.46e^0.029^t	0.023	1.33	0.554
	W	24	R_s = 0.27e^0.062^t	0.102	1.86	0.243
	NW	24	R_s = 0.17e^0.085^t	0.222	2.35	0.064
LG	CKs	24	R_s = 0.60e^0.020^t	0.008	1.22	0.560
	N	24	R_s = 0.54e^0.026^t	0.020	1.30	0.566
	W	24	R_s = 0.23e^0.069^t	0.141	2.00	0.204
	NW	24	R_s = 0.24e^0.075^t	0.193	2.11	0.097
MG	CKs	24	R_s = 0.51e^0.026^t	0.012	1.29	0.511
	N	24	R_s = 0.38e^0.041^t	0.051	1.51	0.369
	W	24	R_s = 0.25e^0.069^t	0.153	2.00	0.170
	NW	24	R_s = 0.17e^0.088^t	0.244	2.41	0.062
HG	CKs	24	R_s = 0.71e^0.012^t	0.003	1.13	0.546
	N	24	R_s = 0.36e^0.039^t	0.045	1.47	0.412
	W	24	R_s = 0.29e^0.060^t	0.135	1.83	0.147
	NW	24	R_s = 0.25e^0.074^t	0.213	2.09	0.072

Table 3 Relationship between soil respiration rate (Rs) and soil moisture content Ws in a Nei Mongol desert steppe

放牧强度 Grazing intensity	处理 Treatment	n	方程 Equation	R²	p
CK	CKs	24	R_s = 0.12W_s - 0.35	0.44	<0.001
	N	24	R_s = 0.09W_s - 0.02	0.30	<0.001
	W	24	R_s = 0.08W_s + 0.19	0.28	<0.001
	NW	24	R_s = 0.08W_s + 0.10	0.34	<0.001
LG	CKs	24	R_s = 0.14W_s - 0.46	0.46	<0.001
	N	24	R_s = 0.09W_s + 0.12	0.29	<0.001
	W	24	R_s = 0.08W_s + 0.29	0.24	<0.001
	NW	24	R_s = 0.09W_s + 0.23	0.34	<0.001
MG	CKs	24	R_s = 0.13W_s - 0.34	0.40	<0.001
	N	24	R_s = 0.11W_s - 0.08	0.36	<0.001
	W	24	R_s = 0.11W_s - 0.04	0.32	<0.001
	NW	24	R_s = 0.10W_s - 0.15	0.44	<0.001
HG	CKs	24	R_s = 0.10W_s - 0.05	0.34	<0.001
	N	24	R_s = 0.08W_s + 0.18	0.25	<0.05
	W	24	R_s = 0.09W_s + 0.01	0.31	<0.001
	NW	24	R_s = 0.08W_s + 0.31	0.28	<0.001

References 68

[1]	Aanderud ZT, Schoolmaster DR, Lennon JT (2011). Plants mediate the sensitivity of soil respiration to rainfall variability. Ecosystems, 14, 156-167. DOI URL
[2]	Ammann C, Flechard CR, Leifeld J, Neftel A, Fuhrer J (2007). The carbon budget of newly established temperate grassland depends on management intensity. Agriculture, Ecosystems & Environment, 121, 5-20.
[3]	Amurijirigala, Hong M, Han GD, Gao FG, Zhao B, Liu CC (2013). Effects of different grazing intensity on soil respiration in the Stipa breviflora desert steppe. Chinese Journal of Soil Science, 44, 321-327.
	[ 阿木日吉日嘎拉, 红梅, 韩国栋, 高福光, 赵巴音那木拉, 刘超川 (2013). 不同放牧强度对短花针茅荒漠草原土壤呼吸的影响. 土壤通报, 44, 321-327.]
[4]	Birch HF (1958). The effect of soil drying on humus decomposition and nitrogen availability. Plant and Soil, 10, 9-31.
[5]	Bond-Lamberty B, Thomson A (2010). Temperature-associated increases in the global soil respiration record. Nature, 464, 579-582.
[6]	Bremer DJ, Ham JM, Owensby CE, Knapp AK (1998). Responses of soil respiration to clipping and grazing in a tallgrass prairie. Journal of Environmental Quality, 27, 1539-1548.
[7]	Cao GM, Tang YH, Mo WH, Wang YS, Li YN, Zhao XQ (2004). Grazing intensity alters soil respiration in an alpine meadow on the Tibetan Plateau. Soil Biology & Biochemistry, 36, 237-243.
[8]	Casals P, Romanya J, Cortina J, Bottner P, Couteaux MM, Vallejo VR (2000). CO₂ efflux from a Mediterranean semi-arid forest soil. I. Seasonality and effects of stoniness. Biogeochemistry, 48, 261-281. DOI URL
[9]	Chen J, Zhou XH, Wang JF, Hruska T, Shi WY, Cao JJ, Zhang BC, Xu GX, Chen YZ, Luo YQ (2016). Grazing exclusion reduced soil respiration but increased its temperature sensitivity in a meadow grassland on the Tibetan Plateau. Ecology & Evolution, 6, 675-687.
[10]	Chen JB, Hou FJ, Chen XJ, Wan XL, Millner J (2015). Stocking rate and grazing season modify soil respiration on the Loess Plateau, China. Rangeland Ecology & Management, 68, 48-53.
[11]	Conant RT, Dalla-Betta P, Klopatek CC, Klopatek JM (2004). Controls on soil respiration in semiarid soils. Soil Biology & Biochemistry, 36, 945-951.
[12]	Conant RT, Klopatek JM, Klopatek CC (2000). Environmental factors controlling soil respiration in three semiarid ecosysterms. Soil Science Society of America Journal, 64, 383-390.
[13]	Davidson EA, Belk E, Boone RD (1998). Soil water content and temperature as independent or confounded factors controlling soil respiration in a temperate mixed hardwood forest. Global Change Biology, 4, 217-227. DOI URL
[14]	Deng Y, Liu XN, Yan RR, Wang X, Yang GX, Ren ZC, Xin XP (2013). Soil respiration of Hulunber meadow steppe and response of its controlling factors to different grazing intensities. Acta Prataculturae Sinica, 22(2), 22-29.
	[ 邓钰, 柳小妮, 闫瑞瑞, 王旭, 杨桂霞, 任正超, 辛晓平 (2013). 呼伦贝尔草甸草原土壤呼吸及其影响因子对不同放牧强度的响应. 草业学报, 22(2), 22-29.]
[15]	Diao LW, Li P, Liu WX, Xu S, Qiao CL, Zeng H, Liu LL (2018). Response of plant biomass to nitrogen addition and precipitation increasing under different climate conditions and time scales in grassland. Chinese Journal of Plant Ecology, 42, 818-830.
	[ 刁励玮, 李平, 刘卫星, 徐姗, 乔春连, 曾辉, 刘玲莉 (2018). 草地生态系统生物量在不同气候及多时间尺度上对氮添加和增雨处理的响应. 植物生态学报, 42, 818-830.]
[16]	Diemer M (1997). Effects of elevated CO₂ on gas exchange characteristics of alpine grassland. Acta Oecologica, 18, 177-182.
[17]	Dong YS, Qi YC, Liu JY, Geng YB, Manfred D, Yang XH, Liu LX (2005). Variation characteristics of soil respiration fluxes in four types of grassland communities under different precipitation intensity. Chinese Science Bulletin, 50, 583-591. DOI URL
[18]	Fu G, Zhang XZ, Yu CQ, Shi PL, Zhou YT, Li YL, Yang PW, Shen ZX (2014). Response of soil respiration to grazing in an alpine meadow at three elevations in Tibet. The Scientific World Journal, 20, 265142. DOI: 10.1155/2014/265142.
[19]	Gao XF, Wu CY, Han GD (2010). Effect of grazing on several ecological factors of the soil in typical steppe. Journal of Arid Land Resources and Environment, 24(4), 130-133.
	[ 高雪峰, 武春燕, 韩国栋 (2010). 放牧对典型草原土壤中几种生态因子影响的研究. 干旱区资源与环境, 24(4), 130-133.]
[20]	Gao YZ, Giese M, Lin S, Sattelmacher B, Zhao Y, Brueck H (2008). Belowground net primary productivity and biomass allocation of a grassland in Inner Mongolia is affected by grazing intensity. Plant and Soil, 307, 41-50.
[21]	Grandy AS, Sinsabaugh RL, Neff JC, Stursova M, Zak DR (2008). Nitrogen deposition effects on soil organic matter chemistry are linked to variation in enzymes, ecosystems and size fractions. Biogeochemistry, 91, 37-49.
[22]	Guo MY, Wei ZJ, Xu LJ, Yang GX, Liu HM, Wu YL, Xin XP (2011). Soil respiration of different mowing types of meadows. Acta Agrestia Sinica, 19, 51-57.
	[ 郭明英, 卫智军, 徐丽君, 杨桂霞, 刘红梅, 吴艳玲, 辛晓平 (2011). 不同刈割年限天然草地土壤呼吸特性研究. 草地学报. 19, 51-57.]
[23]	Hagedorn F, Joos O (2014). Experimental summer drought reduces soil CO₂ effluxes and DOC leaching in Swiss grassland soils along an elevational gradient. Biogeochemistry, 117, 395-412.
[24]	Harrison AF, Taylor K, Scott A, Poskitt J, Benham D, Grace J, Chaplow J, Rowland P (2008). Potential effects of climate change on DOC release from three different soil types on the Northern Pennines UK: Examination using field manipulation experiments. Global Change Biology, 14, 687-702. DOI URL
[25]	Hooper DU, Johnson L (1999). Nitrogen limitation in dryland ecosystems: Responses to geographical and temporal variation in precipitation. Biogeochemistry, 46, 247-293.
[26]	Hou XY (2005). Grassland Ecology and Environment Construction Strategy in China. China Agriculture Press, Beijing. 38-49.
	[ 侯向阳 (2005). 中国草地生态环境建设战略研究. 中国农业出版社, 北京. 38-49.]
[27]	Hou XY, Wang Z, Michael SP, Ji L, Yun XJ (2014). The response of grassland productivity, soil carbon content and soil respiration rates to different grazing regimes in a desert steppe in northern China. The Rangeland Journal, 36, 573-582.
[28]	Jia BR, Zhou GS, Wang FY, Wang YH (2005). Soil respiration and its influencing factors at grazing and fenced typical Leymus chinensis steppe, Nei Mongol. Environmental Science, 26, 3-9.
	[ 贾丙瑞, 周广胜, 王风玉, 王玉辉 (2005). 放牧与围栏羊草草原土壤呼吸作用及其影响因子. 环境科学, 26, 3-9.]
[29]	Klumpp K, Fontaine S, Attard E, Attard E, Le Roux X, Gleixner G, Soussana JF (2009). Grazing triggers soil carbon loss by altering plant roots and their control on soil microbial community. Journal of Ecology, 97, 876-885.
[30]	Kutesch WL, Kappen L (1997). Aspects of carbon and nitrogen cycling in soils of Bornhöved Lake district. II. Modelling the influence of temperature increase on soil respiration and organic carbon content in arable soils under different managements. Biogeochemistry, 39, 207-224.
[31]	Li JZ, Lin S, Taube F, Pan QM, Dittert K (2011). Above and belowground net primary productivity of grassland influenced by supplemental water and nitrogen in Inner Mongolia. Plant and Soil, 340, 253-264.
[32]	Li LH, Wang QB, Bai YF, Zhou GS, Xing XR (2000). Soil respiration of a Leymus chinensis grassland stand in the Xilin river basin as affected by over-grazing and climate. Acta Phytoecologica Sinica, 24, 680-686.
	[ 李凌浩, 王其兵, 白永飞, 周广胜, 邢雪荣 (2000). 锡林河流域羊草草原群落土壤呼吸及其影响因子的研究. 植物生态学报, 24, 680-686.]
[33]	Li MF, Dong YS, Qi YC, Geng YB, Lü Y (2003). The analysis of diurnal variation of CO₂ flux in Leymus chinensis grassland of Xilin River Basin. Grassland of China, 25, 9-14.
	[ 李明峰, 董云社, 齐玉春, 耿元波, 吕晔 (2003). 锡林河流域羊草群落春季CO₂排放日变化特征分析. 中国草地, 25, 9-14.]
[34]	Li XD, Zhang CP, Fu H, Guo D, Song XR, Wan CG, Ren JZ (2013). Grazing exclusion alters soil microbial respiration, root respiration and the soil carbon balance in grasslands of the Loess Plateau, northern China. Soil Science and Plant Nutrition, 59, 877-887. DOI URL
[35]	Li XK, Lu JW, Chen F (2008). Primary study on fertilizer application of forage. Acta Prataculturae Sinica. 17(2), 136-142.
	[ 李小坤, 鲁剑巍, 陈防 (2008). 牧草施肥研究进展. 草业学报, 17(2), 136-142.]
[36]	Li YL, Hong M, Bai WM, Han GD, Wang HM, Zhou M (2015). The responses of soil respiration to water and nitrogen in Stipa breviflora steppe. Acta Ecologica Sinica, 35, 1727-1733.
	[ 李寅龙, 红梅, 白文明, 韩国栋, 王海明, 周萌 (2015). 水、氮控制对短花针茅草原土壤呼吸的影响. 生态学报, 35, 1727-1733.]
[37]	Li YQ, Zhao HL, Zhao XY, Zhang TH, Chen YP (2006). Soil respiration, carbon balance and carbon storage of sandy grassland under post-grazing natural restoration. Acta Prataculturae Sinica, 15(5), 25-31.
	[ 李玉强, 赵哈林, 赵学勇, 张铜会, 陈银萍 (2006). 不同强度放牧后自然恢复的沙质草地土壤呼吸、碳平衡与碳储量. 草业学报, 15(5), 25-31.]
[38]	Lin XW, Zhang ZH, Wang SP, Hu YG, Xu GP, Luo CY, Chang XF, Duan JC, Lin QY, Xu B, Wang YF, Zhao XQ, Xie ZB (2011). Response of ecosystem respiration to warming and grazing during the growing seasons in the alpine meadow on the Tibetan Plateau. Agricultural and Forest Meteorology, 151, 792-802.
[39]	Liu LL, Wang X, Lajeunesse MJ, Miao GF, Piao SL, Wan SQ, Wu YX, Wang ZH, Yang S, Li P, Deng MF (2016). A cross-biome synthesis of soil respiration and its determinants under simulated precipitation changes. Global Change Biology, 22, 1394-1405.
[40]	Liu WX, Zhang Z, Wan SQ (2009). Predominant role of water in regulating soil and microbial respiration and their responses to climate change in a semiarid grassland. Global Change Biology, 15, 184-195. DOI URL
[41]	Liu Y, Zhou LR, Miao SJ (2010). Effects of long-term fertilization on mollisoil enzyme activities and microbial respiration. Soil and Fertilizer Sciences in China, (1), 7-10.
	[ 刘妍, 周连仁, 苗淑杰 (2010). 长期施肥对黑土酶活性和微生物呼吸的影响. 中国土壤与肥料, (1), 7-10.]
[42]	Ma T, Dong YS, Qi YC, Xu FL, Peng Q, Jin Z (2009). Effects of grazing on soil respiration in typical Leymus chinensis steppe in Inner Mongolia. Geographical Research, 28, 1040-1046.
	[ 马涛, 董云社, 齐玉春, 徐福利, 彭琴, 金钊 (2009). 放牧对内蒙古羊草群落土壤呼吸的影响. 地理研究, 28, 1040-1046.]
[43]	Mo JM, Zhang W, Zhu WX, Gundersen P, Fang YT, Li DJ, Wang H (2007). Nitrogen addition reduces soil respiration in a mature tropical forest in southern China. Global Change Biology, 14, 403-412.
[44]	Pan QM, Bai YF, Han XG, Yang JC (2005). Effects of nitrogen additions on a Leymus chinensis population in typical steppe of Inner Mongolia. Acta Phytoecologica Sinica, 29, 311-317.
	[ 潘庆民, 白永飞, 韩兴国, 杨景成 (2005). 氮素对内蒙古典型草原羊草种群的影响. 植物生态学报, 29, 311-317.]
[45]	Peng Q, Dong YS, Qi YC, Xiao SS, He YT, Ma T (2011). Effects of nitrogen fertilization on soil respiration in temperate grassland in Inner Mongolia, China. Environmental Earth Sciences, 62, 1163-1171.
[46]	Prieto LH, Bertiller MB, Carrera AL, Olivera NL (2011). Soil enzyme and microbial activities in a grazing ecosystem of Patagonian Monte, Argentina. Geoderma, 162, 281-287.
[47]	Qi YC, Liu XC, Dong YS, Peng Q, He YT, Sun LJ, Jia JQ, Cao CC (2014). Differential responses of short-term soil respiration dynamics to the experimental addition of nitrogen and water in the temperate semi-arid steppe of Inner Mongolia, China. Journal of Environmental Sciences, 26, 834-845.
[48]	Raich JW, Potter CS, Bhagawati D (2002). Interannual variability in global soil respiration, 1980-94. Global Change Biology, 8, 800-812.
[49]	Raich JW, Schlesinger WH (1992). The global carbon dioxide flux in soil respiration and its relationship to vegetation and climate. Tellus B: Chemical ＆ Physical Meteorology, 44(2), 81-99.
[50]	Reichmann LG, Sala OE, Peters DPC (2013). Water controls on nitrogen transformations and stocks in an arid ecosystem. Ecosphere, 4, 1-17.
[51]	Ren HY, Xu ZW, Isbell F, Huang JH, Han XG, Wan SQ, Chen SP, Wang RZ, Zeng DH, Jiang Y, Fang YT (2017). Exacerbated nitrogen limitation ends transient stimulation of grassland productivity by increased precipitation. Ecological Monographs, 87, 457-469.
[52]	Sánchez ML, Ozores MI, López MJ, Collc R, de Torre B, García MA, Pérez I (2003). Soil CO₂ fluxes beneath barley on the central Spanish plateau. Agricultural and Forest Meteorology, 118, 85-95. DOI URL
[53]	Shan D, Han GD, Zhao ML, Wang Z, Han X, Gao FG (2009). The effects of experimental warming and nitrogen addition on soil respiration in desert Steppe. Journal of Arid Land Resources and Environment, 23, 106-112.
	[ 珊丹, 韩国栋, 赵萌莉, 王珍, 韩雄, 高福光 (2009). 控制性增温和施氮对荒漠草原土壤呼吸的影响. 干旱区资源与环境, 23, 106-112.]
[54]	Shi GX, Geng HL, Wang YL, Wang YH, Qi XR (2008). Daily and seasonal dynamics of soil respiration and their environmental controlling factors in Stipa krylovii steppe. Acta Ecologica Sinica, 28, 3408-3416.
	[ 师广旭, 耿浩林, 王云龙, 王玉辉, 齐晓荣 (2008). 克氏针茅(Stipa krylovii)草原土壤呼吸及其影响因子. 生态学报, 28, 3408-3416.]
[55]	Song CC, Liu DY, Yang GS, Song YY, Mao R (2011). Effect of nitrogen addition on decomposition of Calamagrostis angustifolia litters from freshwater marshes of Northeast China. Ecological Engineering, 37, 1578-1582.
[56]	Sowerby A, Emmett BA, Tietema A, Beier C (2008). Contrasting effects of repeated summer drought on soil carbon efflux in hydric and mesic heathland soils. Global Change Biology, 14, 2388-2404.
[57]	Sowerby A, Emmett BA, Williams D, Beier C, Evans CD (2010). The response of dissolved organic carbon (DOC) and the ecosystem carbon balance to experimental drought in a temperate shrubland. European Journal of Soil Science, 61, 697-709. DOI URL
[58]	Sponseller RA (2007). Precipitation pulses and soil CO₂ flux in a Sonoran desert ecosystem. Global Change Biology, 13, 426-436.
[59]	Stark S, Männistö MK, Ganzert L, Tiirola M, Häggblom MM (2015). Grazing intensity in subarctic tundra affects the temperature adaptation of soil microbial communities. Soil Biology & Biochemistry, 84, 147-157. DOI URL
[60]	Steduto P, Çetinkökü Ö, Albrizio R, Kanber R (2002). Automated closed-system canopy-chamber for continuous field-crop monitoring of CO₂ and H₂O fluxes. Agricultural and Forest Meteorology, 111, 171-186.
[61]	Wang YH, Song XH, Wang ZW, Kang J, Han GD, Wang ZW (2018). Response of plant community diversity and productivity on different stocking rates. Chinese Journal of Grassland, 40(6), 107-112.
	[ 王悦骅, 宋晓辉, 王占文, 康静, 韩国栋, 王忠武 (2018). 植物群落多样性和生产力对不同载畜率的响应. 中国草地学报, 40(6), 107-112.]
[62]	Wang YS, Ji BM, Huang Y, Hu YQ, Wang YF (2001). Effects of grazing and cultivating on emission of nitrous oxide, carbon dioxide and uptake of methane from grasslands. Environmental Science, 22(6), 7-13.
[63]	Weltzin JF, Loik ME, Schwinning S, Williams DG, Fay PA, Haddad BM, Harte J, Huxman TE, Knapp AK, Lin GH, Pockman WT, Shaw MR, Small EE, Smith MD, Smith SD, Tissue DT, Zak JC (2003). Assessing the response of terrestrial ecosystems to potential changes in precipitation. BioScience, 53, 941-952. DOI URL
[64]	Xu LK, Baldocchi DD, Tang JW (2004). How soil moisture, rain pulses, and growth alter the response of ecosystem respiration to temperature. Global Biogeochemical Cycles, 18(4), 1-10.
[65]	Yan LM, Chen SP, Huang JH, Lin GH (2010). Differential responses of auto- and heterotrophic soil respiration to water and nitrogen addition in a semiarid temperate steppe. Global Change Biology, 16, 2345-2357.
[66]	Yan LM, Chen SP, Huang JH, Lin GH (2011). Water regulated effects of photosynthetic substrate supply on soil respiration in a semiarid steppe. Global Change Biology, 17, 1990-2001.
[67]	Zhang L, Huang JH, Bai YF, Han XG (2009). Effects of nitrogen additions on net nitrogen mineralization in Leymus chinensis grassland, Inner Mongolia, China. Chinese Journal of Plant Ecology, 33, 563-569.
	[ 张璐, 黄建辉, 白永飞, 韩兴国 (2009). 氮素添加对内蒙古羊草草原净氮矿化的影响. 植物生态学报, 33, 563-569.]
[68]	Zhou LY, Zhou XH, Zhang BC, Lu M, Luo YQ, Liu LL, Li B (2014). Different responses of soil respiration and its components to nitrogen addition among biomes: A meta- analysis. Global Change Biology, 20, 2332-2343. DOI URL