The Studies On The Responses Of Nematode Communities On Fertilization And Grassing On Eastern Tibetan Plateau Alpine Meadows

Tibetan plateau is one of the important parts of grassland ecosystem and plays an important role in supporting diverse species of plants and animals and in regulating the storage of carbon and nitrogen. However, grassland degradation on the Tibetan plateau induced by overgrazing has become a serious issue, and the available grassland area is considered as being degraded.Among soil fauna, soil nematodes represent one of the most abundant groups of soil fauna in terrestrial ecosystems, and their special characteristics make them as an ideal bioindicators for below-ground ecosystem. Soil nematode communities include genera at most trophic levels, and play critical roles in controlling organic matter decomposition, nutrient cycling and thus in the availability of plant nutrients. At the end of the last century, nematode families were classified along colonizer-persister continuum. According to these conceptual advances, nematode faunal analyses were modified and include the maturity index, the development of an enrichment-structure weighting system, and nematode channel ratio. These particular indices of analysis of soil nematode community promote bioassessment studies using nematodes as indicators.Our study was carried out to understand the human disturbance induced changes in the nematode communities. We focus on the nematode communities composition and structure under typical alpine meadow and swamp meadow where get human disturbance such as grazing and fertilization. We also discussed the pathway that the effects of grazing and fertilization on the soil nematode communites. Further, the main aim of this study was to: 1) determine whether the abundance and structure of nematode communities are affected by grazing and fertilization, 2) evaluate the relationships between environment variable and soil nematodes communities. 3) discuss the pathway that the effects of grazing and fertilization on the soil nematode communites.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. Maturity decreased as grazing intensity increase. The reason of decreased maturity and structure index is a decrease in predators or omnivores accompanied by an increase in the proportion of bacterivores belonging to Cephalobidae and fungivores belonging to Aphelenchoididae.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.Our long-term field experiment of fertilizer addition on typical alpine meadow grasskand supports our research hypotheses and highlights the positive effect of high levels of fertilizer on nematode community abundance. High fertilization treatment significantly increased the number of bacterivores compared with unfertilized control on two sampling dates. The nematode community biodiversity and the value of mature index were significantly reduced by high fertilization treatment, and showed the steadily decrease tendency with increasing fertilizer inputs on two sampling dates. Our Structural Equation Modeling esults successfully elucidated the causal relationships among our experimental variables. For the Structural Equation Modeling model of fertilization effects on soil nematode community compositions, we found that the plant communities determined the soil nematode communities.