Direct And Indirect Impacts Of Different Dominant Plants On Soil Nematode Community In Alpine Meadow

Belowground communities,which play an important role in maintaining biodiversity and ecosystem functions,have been shown to strongly relate to both identity and diversity of aboveground plants.However,how aboveground plants directly and indirectly,via biotic and abiotic factors,affect the belowground communities still poorly understood.Soil nematodes are an important part of soil communities,occupying multiple trophic levels in soil food webs,and have been proposed play an important role in maintaining the function of soil communities.In this study,we established a plant removal experiment to better understand the effects of dominant plant species,Dasiphora fruticosa and graminoids,on nematode assemblages in an alpine meadow on the Tibetan plateau.We quantified soil microbial assemblage structure and edaphic properties to explore how the dominant shrub and graminoids affect nematode communities at both communities level and feeding-type level using structural equation modeling(SEM).We found,1.Dasiphora fruticosa and graminoids have different effects on soil physical and chemical properties.The presence of graminoids increased soil organic carbon content and soil ammonium nitrogen content,but the presence of D.fruticosa reduced soil ammonium nitrogen content.In addition,soil organic carbon and soil total nitrogen are slightly affected by the interaction between D.fruticosa and graminoids.However,other soil properties were not significantly affected by D.fruticosa,graminoids and their interaction.2.Dasiphora fruticosa and graminoids have different impacts on soil microbial communities.Graminoids increased bacterial richness,bacterial diversity and fungal diversity.However,there were no significant effects of D.fruticosa on richness and diversity of bacteria and fungi.Moreover,the removal of D.fruticosa and graminoids didn't change the composition of the bacterial communities;however,the interaction between D.fruticosa and graminoids can significantly affect the composition of the fungal communities.3.Soil nematode communities have inconsistent responses to the removal of D.fruticosa and graminoids.At the community level,the abundance,richness and community composition of nematodes were only significantly affected by the interaction between D.fruticosa and graminoids.The result of RDA showed that only soil water content can significantly affect soil nematode community compositions.At the feeding-type level,the abundance,richness and diversity of nematodes have large differences in response to the removal of D.fruticosa and graminoids.Specifically,graminoids significantly increased the abundance and richness of bacterial-feeding nematodes,as well as the abundance of omnivorous nematodes.Dasiphora fruticosa significantly increased the abundance of fungal-feeding nematodes and the diversity of predatory.The interaction between D.fruticosa and graminoid significantly affected the diversity of fungal-feeding nematodes,while the abundance,richness and diversity of plant-feeding nematodes had no significant responses to effects of D.fruticosa,graminoid and their interaction.4.The direct and indirect effects of D.fruticosa and graminoids on soil nematodes were different.At the community level,graminoids directly affected on soil nematode richness.However,D.fruticosa and the interaction between D.fruticosa and graminoids had no direct effects on the soil nematode richness.D.fruticosa and the interaction between D.fruticosa and graminoids had significant effects on the richness of nematodes by via increasing or decreasing soil organic carbon.By contrast,graminoids didn't affect soil nematode richness indirectly.At the feeding-type level,D.fruticosa significantly reduced the richness of bacterial-feeding nematode,omnivorous and carnivorous by reducing soil organic carbon and bacterial richness.And the interaction between D.fruticosa and graminoids significantly increased the richness of bacterial-feeding nematode,omnivorous and carnivorous by increased soil organic carbon and bacterial richness.Meanwhile,graminoids had significant effects on nematode richness through bacterial richness.Neither plant-feeding nematodes nor fungal-feeding nematodes were significantly affected by the removal of D.fruticosa and graminoids.Our results suggest that dominant plants,such as D.fruticosa and graminoids,in alpine meadows have strong influences on richness,diversity and composition of soil nematode communities.These differences can be attributed to highly changes in soil physical and chemical properties and soil microbial communities.The negatively direct effect of positively indirect effect of dominant plants on soil nematode community indicating the vegetative degradation under global changes may have complicated effects on soil biodiversity.Our research revealed the direct and indirect pathways and mechanisms of dominant plants affecting soil nematode communities.It provides us a better understanding of above-and below-ground linkages,which are of help to predict the changes of ecosystem functions as a result of vegetative degradation.