Diversity And Spatial Distribution Of Soil Fauna Community In Alpine Grassland On The Eastern Edge Of Qinghai-Tibetan Plateau

Soil fauna are an important part of grassland ecosystem and are highly sensitive to environmental changes.In order to figure out the response of soil microarthropod communities to alpine grassland degradation and altitude,alpine grassland with nondegraded(NDG),lightly degraded(LDG),moderately degraded(MDG)and severely degraded(SDG)were selected in the eastern edge of Qinghai-Tibetan Plateau,Soil microarthropods,soil nematode communities,plant communities and soil properties were investigated in July 2019,2020 and 2021.The soil samples(0~20 cm)in the experimental fields were collected by soil drill method.Soil microarthropods were separated by Tullgren method,and soil nematodes were separated by Baermann method.The results showed as follows:1)A total of 2236 soil microarthropods were isolated,belonging to 4 classes,24 orders,157 families,244 classes(genera),and there was no dominant group at the genus level.A total of 339130 soil nematodes were isolated,belonging to 171 genera,59 families,9 orders,2 classes,with an average density of 2512/100 g dry soil.There was no dominant group at the genus level.2)The community composition,structure and diversity of soil microarthropods and soil nematodes were different in the alpine grassland at different degradation stages.During the degradation process,the community density,group number and Shannon Wiener diversity index increased firstly and then decreased(P<0.01);while simpson dominance index decreased firstly and then increased(P<0.01);The increase of altitude significantly reduced the group number and Shannon index of soil microarthropod and soil nematode communities(P<0.01),but there was no significant effect on the density of soil microarthropod communities(P>0.05).3)Grassland degradation and altitude change can affect the structural composition of soil microarthropod and soil nematode communities,and the changes are more obvious between NDG and SDG,low altitude and high altitude.4)Soil organic carbon(SOC),humidity,total nitrogen(TN),p H,plant community height and species number were the main factors affecting the density and diversity of soil microarthropod community(P<0.01,or 0.05).The main environmental factors affecting soil nematode community with different degradation degrees were plant community height,species number,soil p H and organic carbon(P<0.01 or 0.05);The main environmental factors affecting soil microarthropod community at different altitude gradients were plant species number,soil bulk density(BD)and organic carbon(P<0.01 or 0.05).The main environmental factors affecting soil nematode community were plant community height and aboveground biomass(P<0.01,or 0.05).5)The degradation of grassland caused the continuous decrease of the density of bacterial eating nematodes,and the other three nutritional groups increased first and then decreased.The change of enrichment index(EI)showed that MDG could improve the antiinterference ability of soil food web.The results showed that grassland degradation had a sustained inhibitory effect on bacterial nematodes,and promoted and then inhibited fungal nematodes,plant parasitic nematodes and omnivorous nematodes.The results showed that the composition,density and diversity of soil microarthropod and soil nematode communities were sensitive to the degradation of alpine grassland,and affected by environmental factors such as vegetation and soil.The density of bacterial eating nematodes decreased continuously in the process of degradation,which can be used as an indicator of alpine grassland degradation.