氮添加对昆仑山高山草地土壤、微生物和植物生态化学计量特征的影响

全球范围内的氮沉降增加改变了生态系统氮(N)素循环过程,由此带来的生态学效应已成为当前研究的热点。以昆仑山高山草地生态系统2种优势植物黄花棘豆(Oxytropis ochrocephala)和针茅(Stipa capillata)为研究对象,开展人工氮肥添加试验,研究土壤-微生物-植物系统各组分生态化学计量特征对氮添加的响应特征。结果表明:①氮添加显著提高了土壤NH4^+-N和土壤NO3^--N含量(P<0.05),土壤全N、全磷(P)、速效P含量没有明显变化。②氮添加条件下针茅叶片N含量增加,P含量降低,而黄花棘豆N和P含量无明显变化。③土壤微生物量碳(MBC)和微生物量氮(MBN)随着施氮量的增加呈现出先增加后降低的趋势,当施氮量为6N·m^-2·y^-1时呈现出最高值。土壤NH4+-N含量与土壤微生物量N含量有显著的正相关关系(P<0.01)。综合分析表明,短期氮添加有利于土壤养分和微生物量的积累,促进植物和微生物养分吸收利用。2种优势植物的生态化学计量特征对氮沉降的响应不同,过量的氮输入将会造成植物生长受到P限制,氮沉降会改变昆仑山高山草地生态系统的生物地球化学循环过程。

Responses of soil,microbes and plant ecological stoichiometric characteristics to nitrogen addition in an alpine grassland of Kunlun Mountain

The increase of nitrogen deposition worldwide changes the nitrogen cycle of the ecosystem,and becomes the focus on current research.Two dominant plants(Oxytropis ochrocephala)and(Stipa capillata)of alpine grassland ecosystem in the Kunlun Mountain were accounted for the research in this study.The experiment of nitrogen addition was to explore the response of the ecololgical stoichiometric characteristics of soil,microorganism and plant system components.The results showed that:nitrogen addition significantly increased soil NH4^+-N and soil NO3^--N,but soil total nitrogen content,phosphorus content and soil available P content had no significant change.Under the conditions of nitrogen addition,it increased the leaf N contents of S.capillata and decreased the leaf P content.However,the leaf N contents and leaf P contents of O.ochrocephala had no obvious variation.With the increasing of nitrogen addition,soil microbial biomass carbon(MBC)and soil microbial biomass nitrogen(MBN)showed the maximum when nitrogen fertilizer rate was 6 N·m^-2·y^-1.Soil NH4^+-N had positive correlations with MBN(P<0.01).The results showed that it was beneficial to the accumulation of soil nutrients and microbial biomass by short-term nitrogen addition,and it promoted nutrient absorption of plant and microorganisms.The ecological stoichiometric characteristics of the two dominant plants had different responses to nitrogen addition.Excessive nitrogen input induced P deficiency in two dominant plant species,and affected the biogeochemical cycles of alpine grassland ecosystem in the Kunlun Mountain.