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	Plant and soil responses of an alpine steppe on the Tibetan Plateau to multi-level nitrogen addition
	Liu Y. W. ; Xu Ri ; Xu X. L. ; Wei D. ; Wang Y. H. ; Wang Y. S.
	2013
关键词	N:P stoichiometry Nisotope fractionation N limitation N saturation N-use efficiency N-uptake efficiency extensively managed grassland everest ice core terrestrial ecosystems nutrient limitation natural-abundance global change semiarid grassland ammonium record critical loads n-2 fixation
英文摘要	Although plant growth in alpine steppes on the Tibetan Plateau has been suggested to be sensitive to nitrogen (N) addition, the N limitation conditions of alpine steppes remain uncertain. After 2 years of fertilization with NH4NO3 at six rates (0, 10, 20, 40, 80 and 160 kg N ha(-1) yr(-1)), the responses of plant and soil parameters as well as N2O fluxes were measured. At the vegetation level, N addition resulted in an increase in the aboveground N pool from 0.5 +/- 0.1 g m(-2) in the control plots to 1.9 +/- 0.2 g m(-2) in the plots at the highest N input rate. The aboveground C pool, biomass N concentration, foliar delta N-15, soil NO3 (-)-N and N2O flux were also increased by N addition. However, as the N fertilization rate increased from 10 kg N ha(-1) yr(-1) to 160 kg N ha(-1) yr(-1), the N-use efficiency decreased from 12.3 +/- 4.6 kg C kg N-1 to 1.6 +/- 0.2 kg C kg N-1, and the N-uptake efficiency decreased from 43.2 +/- 9.7 % to 9.1 +/- 1.1 %. Biomass N:P ratios increased from 14.4 +/- 2.6 in the control plots to 20.5 +/- 0.8 in the plots with the highest N input rate. Biomass N:P ratios, N-uptake efficiency and N-use efficiency flattened out at 40 kg N ha(-1) yr(-1). Above this level, soil NO3 (-)-N began to accumulate. The seasonal average N2O flux of growing season nonlinearly increased with increased N fertilization rate and linearly increased with the weighted average foliar delta N-15. At the species level, N uptake responses to relative N availability were species-specific. Biomass N concentration of seven out of the eight non-legume species increased significantly with N fertilization rates, while Kobresia macrantha and the one legume species (Oxytropics glacialis) remained stable. Both the non-legume and the legume species showed significant N-15 enrichment with increasing N fertilization rate. All non-legume species showed significant increased N:P ratios with increased N fertilization rate, but not the legume species. Our findings suggest that the Tibetan alpine steppes might be N-saturated above a critical N load of 40 kg N ha(-1) yr(-1). For the entire Tibetan Plateau (ca. 2.57 million km(2)), a low N deposition rate (10 kg N ha(-1) yr(-1)) could enhance plant growth, and stimulate aboveground N and C storage by at least 1.1 +/- 0.3 Tg N yr(-1) and 31.5 +/- 11.8 Tg C yr(-1), respectively. The non-legume species was N-limited, but the legume species was not limited by N.
出处	Plant and Soil
卷	373
期	1-2
页	515-529
收录类别	SCI
语种	英语
ISSN号	0032-079X
内容类型	SCI/SSCI论文
源URL	[http://ir.igsnrr.ac.cn/handle/311030/30370]
专题	地理科学与资源研究所_历年回溯文献
推荐引用方式 GB/T 7714	Liu Y. W.,Xu Ri,Xu X. L.,et al. Plant and soil responses of an alpine steppe on the Tibetan Plateau to multi-level nitrogen addition. 2013.

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