禁牧和放牧条件下施氮肥对高寒草甸线虫群落的影响

Effects of nitrogen addition on nematode communities in the grazed and ungrazed alpine meadows

土壤线虫对生态系统的功能与稳定性具有重要指示作用。为查明施氮肥对禁牧和放牧条件下高寒草甸生态系统的影响,2021年4月在川西北红原县境内的围栏观测样地内外分别设置梯度为0 g/m^(2)、20 g/m^(2)、40 g/m^(2)和60 g/m^(2)的氮肥添加实验。于2021和2022年9月对各样地土壤线虫群落和土壤理化性质进行调查。结果表明:(1)连续两年施肥改变了禁牧与放牧高寒草甸土壤线虫群落组成结构及营养结构;(2)线虫的类群数和Shannon指数以禁牧样地显著高于放牧样地,且在禁牧样地随年际变化显著下降,在放牧样地显著上升;线虫密度则以禁牧样地显著低于放牧样地;(3)连续两年施肥显著增加了禁牧与放牧草地的食真菌线虫密度,降低了植食性线虫密度,使营养结构以食细菌和植食性线虫为主转变成以食细菌和食真菌线虫为主;(4)禁牧样地线虫的基础指数显著低于放牧样地,自由生活线虫成熟度指数和结构指数显著高于放牧样地;随着年际变化,放牧样地的基础指数和通道指数呈显著下降,富集指数和结构指数显著增加,而禁牧样地各生态指数均无显著变化。研究表明对放牧条件下的高寒草甸施氮肥有利于提高线虫群落多样性和土壤食物网稳定性。因此,建议对放牧利用下的高寒草甸进行适当施氮肥。

Soil nematodes are widely used as an indicator of the function and stability of terrestrial ecosystems.The experiments were conducted in April 2021,Hongyuan county,Northwestern Sichuan to reveal the effects of nitrogen addition on the ungrazed and grazed alpine meadows.The gradients of nitrogen additions included 0 g/m^(2),20 g/m^(2),40 g/m^(2) and 60 g/m^(2).Soil nematode communities and soil properties were surveyed in September,2021 and 2022.The results showed that:(1)the taxonomic composition and trophic structure of soil nematode communities in the grazed and ungrazed alpine meadows changed during the two continued years of nitrogen addition.(2)The nematode abundance was significantly lower,while the taxonomical richness and Shannon index were significantly higher in the ungrazed than grazed alpine meadows.The taxonomical richness and Shannon index significantly decreased in ungrazed,but significantly increased in grazed alpine meadows with increasing year.(3)Two continued years of nitrogen addition significantly increased the abundance of fungivores,but significantly decreased the abundance plant⁃parasites in the grazed and ungrazed alpine meadows,leading to the dominant trophic groups shifted from the bacterivores and plant⁃parasites to the bacterivores and fungivores.(4)The basal index of nematodes was significantly lower,but the maturity index and structure index were significantly higher in the ungrazed than the grazed alpine meadows.The basal index and channel index decreased significantly,and enrichment index and structure index increased significantly with increasing year in the grazed alpine meadows,with no significant changes observed for the ecological index of nematode communities with increasing year in the ungrazed alpine meadows.The study shows that nitrogen addition can promote the nematode diversity and soil food web stability in the grazed alpine meadows.Therefore,an appropriate amount of nitrogen fertilizer can be added to the grazed alpine meadows.