Effects Of Pika Disturbance On Soil Microbial Community Structure And Assembly Mechanism In Alpine Meadow

Alpine ecosystems play essential roles in maintaining terrestrial ecosystem functions.Because of their unique climatic conditions,the vegetations and soils in such ecosystems are highly vulnerable to external environmental variation.Small burrowing mammals are considered as the "ecosystem engineers",and their excavation and gnawing activities are the key driver of environmental changes in soils.At present,some studies have been carried out on the variations of alpine grassland ecosystem under the disturbance of burrowing mammals.However,most of studies mainly focus on the changes of vegetation and soil properties,and little is known regarding the evolution of soil microbes which drive the nutrient cycle and energy flow.Taking the patches disturbed by pika(Ochtona curzoniae)in the alpine meadow of Qinghai-Tibet Plateau as the object,this study systematically analyzed the changes of microbial community structure and functions and their drivers under the disturbance of pika,and clarified the distribution pattern and formation mechanism of microbial diversity in patches by using microbial amplicon sequencing technology.This study provides a basis for further revealing the mechanism of biodiversity maintenance and functional stability of alpine ecosystem.The main results are as follows:(1)Effects of pika disturbance on soil microbial structure and co-occurrence networkPika disturbance promoted the enrichment of bacterial nitrification and denitrification groups,increased the transmission risk of fungal animal and plant pathogens,and led to the decrease of relative abundance of nitrogen fixing bacteria and mycorrhizal fungi.The change of relative abundance of these functional groups was closely related to the decrease of dissolved organic carbon and water content and p H and the increase of available nutrients(available phosphorus,available potassium and inorganic nitrogen).The variations of these soil variables were caused by the decrease of aboveground vegetation coverage and soil compactness after pika interference.Compared to the undisturbed soils,the richness of bacteria and fungi in the disturbed soils increased by 37.2% and 130.7%respectively,and their Shannon diversity index increased by 16.6% and 34.6% respectively,which further led to the increased complexity of soil bacterial and fungal networks in disturbed soils.The increase of microbial alpha diversity and network complexity was also related to the enhancement of soil available nutrients.The keystone species identified in disturbed soils belongs to phyla Actinobacteriota,Proteobacteria,and Ascomycota,while the keystone species identified in undisturbed soils mostly belongs to phyla Acidobacteriota and Ascomycota.These keystone taxa could be used as an indicator of the effects of subterranean mammalian engineers on alpine ecosystems.(2)Changes of soil microbial community structure and co-occurrence network on pika-disturbed patchesWith the increase of disturbed patch area,the alpha diversity of bacteria decreased significantly,while the beta diversity of fungi increased significantly.These strikingly different species-area relationship was closely associated with their community assembly mechanisms.The loss of bacterial diversity on larger patches was largely driven by deterministic processes,mainly due to the poor soil quality(decline of soil organic carbon,total nitrogen,available nutrient and moisture contents).In contrast,fungal distribution was driven primarily by stochastic processes that dispersal limitation contributed to their higher fungal diversity on lager patches.Additionally,bacteria and fungi both form a complex community to resist pika disturbance as patch area increased,but bacteria tended to form a closer-association community while fungi tended to construct a higher-modularity community.The relative importance of stochastic and deterministic processes was an important factor driving the variations of bacterial and fungal network structure.In conclusion,pika disturbance enhanced the alpha diversity and network complexity of soil bacteria and fungi,promoted the enrichment of bacterial nitrification and denitrification groups and fungal animal and plant pathogens,and reduces the abundance of nitrogen fixing bacteria and mycorrhizal fungi.With the increase of patch area,the soil bacterial diversity decreased significantly,while the fungal diversity increased.The above results reveal the response and mechanism of alpine soil microbial community to pika disturbance,which can provide a basis for the maintenance of alpine ecosystem functions and soil biodiversity.