氮素添加对青藏高原高寒草甸植物群落物种丰富度及其与地上生产力关系的影响

Effects of nitrogen addition on species richness and relationship between species richness and aboveground productivity of alpine meadow of the Qinghai-Tibetan Plateau,China

植物种群对有限资源的竞争是决定植物群落物种组成、多样性和生产力等群落结构和功能的主要因素。该文以青藏高原高寒草甸为研究对象,研究了短期内不同水平的氮素添加对高寒草甸植物群落的影响。结果表明:1)氮素添加提高了土壤中NO3–-N等可利用资源的含量,增加了植物群落植被的盖度,减小了植被的透光率,随着施氮量的增加,群落中物种丰富度显著降低(p<0.001);2)氮素添加显著改变了植物群落的地上生产力(p<0.05),随着施氮量的增加,地上生产力呈先增加后降低的变化趋势,各功能群中禾草生物量显著增加,而杂类草和豆科植物生物量随施氮量的增加逐渐减少;3)物种多样性与植被透光率呈线性正相关(p<0.05);地上生产力与土壤NO3–-N含量呈线性正相关(p<0.05);物种丰富度与地上生产力之间呈负相关关系。这说明短期内氮素添加通过改变土壤中NO3–-N等可利用资源的含量而对植物群落物种组成和地上生产力产生影响。

Aims Competition for different limiting resources among plant species is the main factor that influences plant community composition,diversity and productivity.Our objective was to investigate the effects of different levels of nitrogen addition on species richness and aboveground productivity of alpine meadow of the Qinghai-Tibetan Plateau,China.Methods We added nitrogen in a completely randomized block design and measured plant aboveground biomass,species composition,vegetation light penetration and soil pH and NO3^--N content in each plot.Regression and analysis of variance were used to analyze the responses of these measures to different levels of nitrogen addition.Important findings Nitrogen addition changed the soil physical and chemical properties,enhancing the content of NO3^--N available resources in the soil,increasing plant cover and reducing vegetation light penetration.With increasing N addition,species richness decreased sharply（p 〈0.001）.N addition changed aboveground productivity significantly（p 〈0.05）.With increasing N addition,aboveground productivity increased first then decreased,and grass biomass increased while forb and legume biomasses decreased.There was a significant linear positive relationship between species richness and vegetation light penetration（p〈 0.05） and also between aboveground productivity and soil NO3^--N content（p 〈0.05）.The relationship between aboveground productivity and species richness was negative.We suggested that the short term effects of nitrogen addition on community composition and aboveground productivity were determined by the changed soil NO3^--N content.