Effects Of Changing Carbon Input Pathways On Soil Microbial Communities In A Temperate Steppe Of Northern China

Grassland ecosystems,accounting for 41% of land area in China,play an important role in wind prevention and sand fixation,soil and water conservation,climate regulation and maintaining biodiversity.Plants influence the structure of soil microbial community through aboveground litter and belowground root exudates.As the driver of biogeochemical cycling processes,soil microorganisms are critical to maintaining ecosystem functions.However,few studies have been focused on the effects of different C input ways on soil microorganisms.Based on a long-term field experiment conducted in Duolun County of Inner Mongolia,litter addition,litter removal,and plant removal were used to explore the influence of different C inputs on the composition and diversity of soil microbial communities(i.e.,bacteria,fungi,and protist)in the temperate grassland.(1)Litter addition increased soil base respiration,but had no effect on soil nitrogenase activity,potential ammonia oxidation or nitrogen mineralization in the temperate steppe.Litter removal had no effect on soil nitrogenase activity,base respiration,potential ammonia oxidation or N mineralization.Plant removal reduced soil nitrogenase activity,base respiration,potential ammonia oxidation and N mineralization.These findings indicate that the decrease of soil dissolved organic C content under plant removal significantly affects the functional activity of soil microorganisms and may reduce the N supply of biological N fixation to grassland ecosystems.(2)Litter addition had no effect on the alpha diversity of the bacteria,fungi,or protist communities.Both plant removal and litter removal reduced the alpha diversity of bacteria and fungi communities,but did not affect the alpha diversity of the protist community.The alpha diversity of bacteria and fungi communities were positively correlated with soil ammonium N and dissolved organic C,respectively.Soil ammonium N and dissolved organic C accounted for 20.6% and 67.2% of alpha diversity of bacteria and fungi communities,respectively.(3)Litter addition,litter removal,and plant removal affected the bacterial community composition,plant removal affected the community composition of fungi and protists.For the bacteria community,the relative abundance of Actinobacteria and Chloroflexi was negatively correlated with soil dissolved organic C,and the relative abundance of Proteobacteria increased with the increase of soil dissolved organic C contents.For the fungi community,the relative abundance of Mortierellomycota increased with the decrease of soil dissolved organic C contents.The relative abundance of Archaeplastida was positively correlated with soil dissolved organic C contents in protist community.(4)There was no difference in the soil microbial network between litter addition and litter removal treatments.Plant removal reduced the number of nodes and edges in soil microbial network comparing with that in plant growth treatments.These findings reveal that plant removal made the network structure of soil microbial communities more unstable and weaker.These results indicate that the alpha diversity of bacteria and fungi communities is more sensitive to litter removal than litter addition.Plant removal decreased the alpha diversity of bacteria and fungi communities,and altered soil microbial community composition and network relationships.These findings reveal the effects and underlying mechanisms of different carbon inputs on soil microbial community,which is of great significance for further understanding the stability of soil microbial communities and element cycling based on microbial community in the context of global change.