短期不同水平氮添加对农牧交错带草地植物群落多样性和生产力的影响

Effects of Short-term Nitrogen Addition on Plant Community Diversity and Productivity of Grassland in Agro-pastoral Ecotone

以晋北农牧交错带半干旱草地生态系统为研究对象,设置8个不同氮添加水平,研究物种多样性和生产力对短期氮添加的响应。结果表明:在不同氮添加水平中,植物群落多度、高度与盖度在添加16gN/m^2时均表现为最高,在32gN/m^2水平下最低;对于物种多样性,16gN/m^2水平下8月的物种多样性最高;随着氮添加水平上升,地上生物量呈抛物线型变化,添加16gN/m^2地上生物量最高,不添加氮时最低;在0~10cm土层中,地下生物量在16gN/m^2添加量水平下最高。表明16gN/m^2氮添加水平是区域饱和氮添加水平,超过这个添加量,地上、地下生产力以及物种多样性开始下降,生态系统的稳定性和初级生产力均降低。

Nitrogen(N) deposition gradually increased in the last 30 years in our country,the increasing of N deposition had effects on the biological diversity,species communities,productivity,structure and function of ecosystem.This experiment was conducted with eight N addition levels in agro-pastoral ecotone in semi-arid grassland of northern Shanxi province.We investigated the coverage,abundance,and species height of each plant community in the fixed quadrat at the beginning of each month (June-August).In addition,above-ground biomass was harvested in mid-August.The purpose of this study was to understand the response of plant community characteristic and above and below ground productivity to short-term nitrogen addition in the semi-arid grassland ecosystem.The results showed that (1) the plant community abundance,height and coverage were the highest at 16g N/m^2 and the lowest at 32g N/m^2,and species diversity was the highest at 16g N/m^2 level in August;(2) with the increase of nitrogen addition level,the aboveground biomass showed a parabolic change.The aboveground biomass with 16g N/m^2 was the highest,and the lowest at no nitrogen addition;(3) In the 0~10cm soil layer,the underground biomass was the highest at the level of 16g N/m^2.It indicated that the nitrogen addition level of 16g N/m^2 was the level of regional saturated nitrogen addition.Above this addition,the above-ground biomass and species diversity began to decline,which reduced ecosystem stability and primary productivity.If this amount was a threshold in the agro-pastoral ecotone or not,we need to conduct a comprehensive assessment of the long-term research results to determine the mechanism of the sustainability of the semi-arid grassland in agro-pastoral ecotone.