Effects Of Grazing And Nitrogen Addition On Soil Nematode Community In Meadow Grassland

Nematodes occupy multi-trophic levels in the soil detrital food web,which exerts a large influence on energy and nutrient cyclings.Moreover,the community structure and diversity of nematode are considered to be related to the function and stability of ecological system.In grassland ecosystems,grazing by large herbivores is the main disturbance to soil,as well as the management for the protection of biodiversity and grassland ecosystem functions.Nitrogen deposition is one of the key issues of global change.Above-ground grazing and nitrogen addition have strong effects on the soil nematodes via their impacts on the plant community,soil nutrients and soil environment in grassland systems.Currently,it has been widely accepted that grazing and nitrogen addition can affect soil nematode communities respectively,while little is known about the combined effects of large herbivores grazing and nitrogen addition.In particular,the effects of grazing assemble(sheep grazing,cattle grazing,mixed grazing)on soil nematode communities are lack of relevant research under nitrogen deposition.In this study,we mainly focused on the research about the effects of single and mixed grazing of large herbivores(Ujumqin oves and Mongolica uaccam)on soil nematode community,soil properties and plant community under the condition of different nitrogen addition levels,in Hulun Buir Meadow Grasslands.The main results are as follows:(1)There were 52 genera in Hulun Buir Meadow Grasslands.The advantage genera among different plots were Acrobeles、Acrobeloides、Helicotylenchus and Filenchus.The common genera were Chiloplacus、Prismatolaimus、Paraphelenchus、Diphtherophora、Tylenchorhynchu、Mononchus and Thonus。(2)The effects of nitrogen addition on nematodes could be affected by grazing assemble.In cattle grazing treatment,nitrogen addition increased the total abundance of soil nematodes by significantly increasing the abundance of bacteria-feeding,herbivorous and omnivorous predator nematodes,while in other grazing assembles,nitrogen addition significantly decreased the total abundance.Nitrogen addition significantly reduced the abundance of fungi-feeding nematodes in all the grazing treatment.Nitrogen addition reduced nematode abundance mainly through reducing plant root biomass.In cattle grazing treatment,nitrogen addition significantly increased the richness and diversity of nematodes,while in other grazing treatments,nitrogen addition significantly decreased richness.Nitrogen addition directly reduced nematode richness,as well as increased richness through improving soil ammonium nitrogen concentration.Nitrogen addition increased the diversity of nematodes by increasing soil nitrate concentration.(3)The effects of grazing on nematodes could be affected by nitrogen.Without nitrogen addition,cattle grazing significantly decreased the abundance of nematodes by decreasing the abundance of bacteria-feeding,herbivorous and omnivorous predator nematodes.In the nitrogen addition plots,cattle grazing significantly increased the abundance of nematodes by increasing the abundance of the above three trophic groups.Without nitrogen addition,the nematode richness in cattle grazing was lower than those in the treatments of no grazing and sheep grazing.The nematode diversity in cattle grazing and mixed grazing was lower than those in the treatments of no grazing and sheep grazing.With nitrogen addition,cattle grazing significantly increased nematode richness,and nematode diversity in cattle grazing and mixed grazing was higher than those in plots of no grazing and sheep grazing.Grazing decreased nematode richness by reducing plant richness.Grazing also reduced nematode diversity by reducing soil nitrate concentration.(4)Mixed grazing could alleviate the adverse effects of nitrogen deposition on the nematode community.In the treatments of no grazing,cattle grazing and sheep grazing condition,nitrogen application significantly increased channel index and decreased maturity index,and in the treatment of mixed grazing nitrogen had no significant effects.Without nitrogen addition,nematode maturity index in mixed grazing was significantly lower than that in other grazing treatments.And after nitrogen fertilization,grazing could significantly increase the maturity index.The results showed that under the background of nitrogen deposition,grazing could improve the stability of nematode community,and mixed grazing could alleviate the adverse effects of nitrogen deposition on nematode community.In conclusion,present study clarified the mechanism of the effects of nitrogen addition and mixed grazing on soil nematodes.It revealed the pathways of nitrogen addition and mixed grazing to regulate nematode communities by changing soil environment and plant communities,as well as clarified the internal mechanism of grazing assemble to regulate the soil nematode communities under the background of nitrogen deposition.Experimental results also showed that the diversity of soil nematodes was positive related to available nitrogen content and plant diversity,it enriched the theory of grassland ecology and biodiversity.Under the background of nitrogen deposition,grazing could improve the stability of nematode community,and mixed grazing could alleviate the adverse effects of nitrogen deposition on nematode community.This study can give deep understanding of the maintain mechanism of structure and function of grassland ecosystem,and its response to global change and human disturbance.