Effects Of Alpine Cushion Plants On Soil Microbial Community Structure And Functions

With the increasing pronounced trend of global warming,the water-heat balance of the alpine environment is constantly changed.Cushion plants are dominant stress-tolerant species with wide distribution in alpine environments.Recently,the nurse effect of the cushions on other aboveground vegetations has been widely concerned.In the alpine belt,the beginning of soil formation occurs at the habitats occupied by cushions and their influence on soil organic matter is crucial.Besides,abiotic conditions,such as soil moisture and temperature,are often improved beneath the dense canopy of cushions,thus,the cushions facilitated the growth and establishment of neighboring plants.In recent years,studies have found that the interaction between cushion and other plant is in a dynamic process,and the interaction is influenced by the phenotype variance of cushions and their canopy area.However,the effects of cushion plants on soil microbial diversity and community structure have been rarely reported.Especially,no relevant studies have been reported on the effect of cushions with a phenotypic variation on the structure and functions of soil bacterial and fungal communities,and the response of soil microbial communities to the canopy-area differences of cushions.The study of distribution pattern and driving factors of soil microbial community in the alpine cushion plant ecosystem is of great theoretical significance for revealing the mechanism of the nurse effect on the underground microbial community.Therefore,Qilian And Tianshan mountains in the western region of our country which are dominated by the nurse cushions Thylacospermum caespitosum and Arenaria kansuensis were selected as the sample areas,the soil samples under the cushions and paired open plots were collected.High-throughput sequencing,Biolog Eco-plate,phospholipid fatty acid(PLFAs),and soil enzymatic activities were employed to systematically study the community structure and functional characteristics of soil bacterial and fungal communities.This study disentangled the phenotypic variation of cushions and abiotic factors of different scales which influenced the structure and functions of soil microbial communities,and the influence of canopy area of cushions on the structure and functional characteristics of microbial communities.The main conclusions are as follows:1)In the alpine cushion plant ecosystem,the variance of soil fungi community was mainly driven by biological factors related to cushion presence and their phenotype variance,especially for the fungal diversity,while the fungal community composition was mainly driven by biotic factors with an equal contribution of cushion presence and cushion phenotype effects;the relative abundance of dominant Mortierellomycota and Basidiomycota was significantly influenced by cushion presence.While the soil bacterial diversity and community composition was mainly driven by the variance of soil p H and hydrothermal conditions.The dominant bacterial taxa,including Proteobacteria,Chloroflexi,Gemmatimonadetes and Firmicutes,were also significantly influenced by the site effect which related to the soil p H and hydrothermal conditions.2)Compared to the effect of phenotypic variation of T.caespitosum on soil microbial functions,the effect of cushion presence was more obvious.Regardless of the phenotype was loose or tight,the carbon utilization ability of the soil microorganisms under the cushions was higher than that of the soil microorganisms at the paired open plots.Especially in the Tianshan field,T.caespitosum showed a significant facilitative effect on the carbon source utilization of soil microorganisms.Among the six kinds of carbon sources in the Biolog Eco-plate,the nurse effect of cushions leads to the metabolic ability of soil microorganisms on amino acids,esters,alcohols,amines,and carboxylic acids substrates were generally higher than the soil microorganisms at paired bare plots.Moreover,only alcohol carbon source utilization activity was significantly affected by the phenotypic variation of cushions.Notably,phenotypic variation of cushions significantly affected the activities of dehydrogenase,phosphatase,and urease.3)The structure of the soil microbial community under the canopy changed significantly as the cushions growing.The bacterial diversity and community composition showed significant differences under the cushions with different canopy areas.With the increasing of cushion canopy area,the soil bacterial diversity increased under the canopy.The relative abundance of dominant taxa,including Planctomycete,Planctomycete,Bacterioidetes,Nitrospirae and Chloroflexi showed significant differences under cushions with different canopy areas.Through the analysis of soil bacterial co-occurrence network,it was found that with the growth of cushions,the interactions between bacterial species became more complex and five key species were found in the sub-network module of large cushion plants.Relatively,although the fungal diversity also showed a trend of a gradual increase,the difference was relatively weak.Additionally,the fungal community composition and relative abundance of dominant taxa were not significantly affected by the canopy area of cushions.The interactions between soil fungal species did not significantly increase with increasing of cushion canopy area.Only one key fungal species was found in the sub-network module of large cushion plants.4)The canopy area of cushions showed an important effect on the functions of both soil bacteria and fungi,especially in the soils under the large cushions,the relative abundance of microorganisms involved in degradation is high.The results showed that cushion presence was the main factor affecting the functional diversity of bacterial communities by the functional prediction.The function of soil bacterial community under the cushions was more similar regardless of the canopy area.Saprotrophs were the main trophic mode for fungal communities.In addition,the abundance of saprophytic fungi under the cushions was higher than soils from bare plots.The relative abundance of wood saprotroph was the highest in the soil under the large cushions and the lowest in bare soil.Our research shows that nurse plants influenced both the microbial community structure and functions,but the effects on bacterial and fungal communities were different.The variance of the soil fungi community was mainly driven by biological factors related to cushions and their phenotype variance.Additionally,with increasing of cushion canopy area,the microbial community structure and functions also changed,among which the response of soil bacterial community structure was more significant.This study explored the impact of cushions on the structure and function of soil microbial community from different perspective,and confirmed that ?-Proteobacteria and Agaricomycetes play key roles in maintaining the stability of the soil bacterial and fungal communities under the cushions.It provides a theoretical basis for further revealing the mechanism of nurse effect and provide theoretical support for illustrating the complex interactions between aboveground and belowground communities,and the ecosystem restoration and promotion of ecosystem service performance.