Nematode communities response to long-term grazing disturbance on tibetan plateau

Grazing by herbivores plays a key role in grassland ecosystems, but its effects on soil fauna biodiversity are not clear in alpine meadow ecosystems, especially on the Tibetan plateau. We investigated the effects of long-term grazing disturbance of varying intensities (low disturbed site, medially disturbed site, and seriously disturbed site) on ecosystem biodiversity and functional process using soil nematode communities. Soil physicochemical characteristics and plant communities were also measured to explore the relationships between soil nematode communities structure and key environment variable. Soil samples were collected in May, June, August, and October, 2013. The abundance of total nematode communities, plant feeders and bacterivores increased with the grazing intensity increase, and predators decreased with grazing intensity increase. Low disturbed site has the lowest abundance of fungivores. Grazing disturbance has no significant influence on abundance of omnivores ( P>0.05). Species richness was highest on seriously disturbed site and lowest on low disturbed site. MI and SI decreased as grazing intensity increase. The highest NCR was found in low disturbed site and the lowest in medially disturbed site. The highest EI was found in medially disturbed site and the lowest in low disturbed site. Principal component analysis (PCA) showed that nematode communities could be separated by three different grazing disturbance intensity sites. Redundancy analysis (RDA) showed that Helicotylenchus, Acrobeloides and Labronema were positively correlated with higher plant communities diversity. Filenchus was positively correlated with forbs biomass. Some omnivores such as Eudorylaimus and Aporcelaimus was positively correlated with soil moisture and rich nutrient resources, meanwhile, Enchodelus and Coomansus was positively correlated with biomass of sedges and grasses. Anaplectus and Prismatolaimus significantly correlated with soil moisture, nutrient resources and biomass of sedges and grasses. This study revealed that grazing herbivores can change composition, structure and diversity of soil nematode communities, and then reflect radical shift in below-ground soil faunal biodiversity and processes in alpine meadow on the Tibetan plateau.