Effects Of Understory Vegetation Removal And Litter Removal On Soil Microbial Community Structure

Understory vegetation and litter together maintain nutrient allocation between aboveground and underground,and affect the stability of soil microbial community structure in forest ecosystems.The understory vegetation removal can reduce the competition of understory vegetation to light and promote the tree growth.Litter removal can accelerate the evaporation and reduce the input of soil organic matter,thus suppress soil microbial activity.Afield experiment with removal of understory plant and/or litter was conducted in a deciduous broadleaved forest of the subtropics-temperate transitional zone in Central China.The experiment has four treatments:control,understory vegetation removal,litter removal,both understory vegetation and litter removal.A total of 16 sample plots were established with 4 replications for each treatment.Understory vegetation removal significantly decreased soil total carbon and soil total nitrogen by 11.5%and 15.7%and substantially reduced soil organic carbon by 12.76%,but soil dissolved organic carbon have no change under the understory vegetation removal.Understory vegetation removal significantly decreased NH₄⁺-N by 12.76%but increased NO₃^--N by 14.59%,respectively.Soil organic carbon was increased by 20.94%,but soil dissolved organic carbon was reduced by 11.02%under the litter removal treatment.Under the litter removal treatment,NH₄⁺-N and NO₃^--N was decreased by 29.3%and39.07%,respectively.Soil microbial biomass carbon microbial biomass nitrogen were decreased and increased by 9.14%and 8.22%,respectively,under the litter removal treatment.There was inter-annual variability in microbial community structure.The contents of fungi,actinomycetes,and gram-negative bacteria and the proportion of fungi to bacteria,gram-negative bacteria,and gram-positive bacteria were significantly increased under the litter removal treatment,but gram-positive bacteria were decreased under the litter removal treatment.The litter removal treatment significantly increased the ratio of fungal to bacteria by 0.03%and 0.07%in 2017 and 2018,and the ratio of gram-negative bacteria to gram-positive bacteria by 0.19%in 2018.The study indicates that the little effect of understory vegetation removal on soil microbial community structure may be related to the sustained supply of organic C from root to soil microbial community.Litter removal showed remarkable effects on the assimilation rate of bacteria and fungi to carbon probably due to it impacts on soil total C,total N,and soil organic C.The understory vegetation removal only removes the surface vegetation but does not remove plant roots,which may continue to maintain soil nutrient cycle and supply microbial growth.The little effect of litter removal on soil microbial community structure in the 3-year suggests that the influence of litter removal on soil might be a slow process.The litter removal had no effect on soil microorganism in the short time.Therefore,there was no response in soil microbial community structure under both the understory plant and litter removal treatments.Understory plant vegetation and litter removal can change soil physical and chemical properties and affect MBC and MBN,thus influence soil microbial community structure.This study is a further improvement and extension of current report on microbial community structure,and will provide strong data support for the response of microbial community structure to changes in C input from plants and aboveground litter.