Study On Soil Fungal Community Structure And The Coupling Relations Between Above-ground And Below-ground To N,P Addition In Alpine Meadow

Soil microorganisms,as the main component of below-ground biological communities,play an important role in the biogeochemical cycle and the connection of above-ground biological communities.Previous studies focused mainly on the changes of above-ground biological communities,ignoring the importance of below-ground biological communities in the ecosystem.The relationship between above-ground and below-ground communities directly affects the functions of ecosystems,as well as the future global climate change and ecological balance.In recent years,more and more attention has been paid to the study of plant-soil-microbial system.Current studies have shown that nitrogen deposition affects the functions of above-ground and below-ground biological communities and ecosystems.However,it is not clear what the direct or indirect interactions between plant-soil-microbial systems are in different types of fertilization treatments.As the"third pole"of the world,the Tibetan Plateau has a unique geographical and ecological environment.High altitude,low temperature,strong radiation and other factors make the region sensitive to global climate change.In recent years,due to the increase of human activities,atmospheric nitrogen deposition in the Tibetan Plateau has become very obvious.Therefore,a thorough understanding of the responses of above-ground and below-ground biological communities to the changes of available nutrients in alpine meadows on the Tibetan Plateau can predict future ecosystem changes and provide theoretical guidance for the formulation of conservation measures.In this study,the alpine meadow soil of Tibetan Plateau was treated with N,P and NP gradient fertilization for four consecutive years.Illumina high-throughput sequencing and qPCR techniques were used to analyze the changes of soil microbial communities.The data of microbial communities were integrated with the physical and chemical properties of above-ground plants and soils,and a coupling model was established to clarify the relationship between plant,microorganism and environment.The mechanism of soil microbial community responding to environmental change and its impact on ecosystem function and stability provide theoretical basis and technical support for the sustainable development of alpine meadow in Tibetan Plateau.The main experimental results are as follows:1.Effects of N,P and NP fertilization on soil fungal communityHigh-throughput sequencing results of soil fungal community showed that298620 optimized sequences and 1486 OTU numbers were obtained from ITS1region sequencing of ITS gene.According to taxonomic notes,soil fungi community can be divided into seven different groups at phylum level.The relative abundance of the main fungi is 57.01%for Ascomycota,13.30%for Basidiomycota and 5.64%for Zygomycota.In NP co-fertilization treatments,the Chao1 index of soil fungi alpha diversity and the numbers of fungi OTU were significantly different among different gradient fertilization treatments.When N or P fertilizer was added separately,the diversity of soil fungi alpha and the number of ITS gene copies of fungi did not change significantly.The changes of soil fungal community structure were analyzed by NMDS and ANOSIM.The results showed that NP co-fertilization significantly affected soil fungal community structure,while N or P alone had no significant effect on soil fungal community structure.2.Effects of environmental factors on soil fungal communityThe effects of soil factors and plant characteristics on soil fungal community structure were studied by RDA and Mantel test.The results showed that pH?r=0.31,P=0.04?was the main factor affecting the fungal community structure.Using all the physical and chemical factors of soil as soil factors,plant biomass and number of plant species as plant factors,VPA analysis showed that both variables had a great impact on fungal community structure,but 34.11%of soil factors alone explained much more than 6.92%of plant factors alone.Spearman correlation analysis showed that there was no significant correlation between alpha diversity of Soil Fungi Community and all soil physical and chemical factors,and there was no significant correlation between ITS gene copy number of soil fungi and the ratio of bacteria/fungi abundance.Regression analysis showed that the relative abundance of Basidiomycota decreased with the increase of nitrate nitrogen content and plant species richness,and increased with the increase of soil pH.When N,P or NP were added alone,there was no significant correlation between the diversity of soil fungi and the diversity of plant communities.When N or P was added alone,there was a significant positive correlation between the diversity of soil fungi and plant species.The relative abundance of soil saprophytic fungi was significantly correlated with soil pH and soil water content.The relative abundance of soil symbiotic fungi increased with the increase of nitrate nitrogen and plant biomass.3.Plant-microbe-soil linkagesStructural equation modeling results showed that N addition directly affected bacterial richness and community composition by changing NO₃^--N content,directly affected archaea and fungi richness by changing soil pH,and indirectly affected archaea,fungi richness and community composition by changing plant species richness.P addition has direct and indirect effects on archaea community,and the increase of AP content directly affects the composition of archaeological community.AP indirectly affects the richness of archaea community by changing plant species richness.For bacteria and fungi,P addition indirectly changes the composition of bacterial and fungal communities by influencing plant species richness.When NP was added,AP directly affected the composition of archaea and fungi communities.AP indirectly affected the composition of archaea and fungi communities by changing above-ground plant biomass.In addition of N or NP,soil NH₄⁺-N concentration is the main factor causing the change of archaea and fungi communities,and NO₃^--N concentration is the main factor causing the change of bacterial communities.Compared with bacteria,archaea and fungi communities are more closely related to the above-ground plant communities.