Effects Of Moso Bamboo Expansion On Soil Microbial Community Structure And Function Of Typical Subtropical Forest

Soil microorganisms,which are the drivers of nutrient and key elements circulation in terrestrial ecosystems,play an important role in the biogeochemical cycle.The structure and function of soil microbial community are affected by human activity,environment and other factors,and are also closely related to vegetation composition and changes.Therefore,the study of soil microorganism structure and function change and its dynamic relationship with vegetation can provide theoretical basis for environmental ecosystem rehabilitations.With abundant bamboo resources in China,bamboo has been widely cultivated for its high economic value.But due to the inadequate management,expansion of bamboo forests and its side effects on the ecosystem are reported in recent years.This study attempts to provide scientific data for management of bamboo forest ecosystem and theoretical basis for environmental restoration of forest ecosystem by studying the effects of bamboo expansion on soil microbial community structure and function,especially rhizosphere microbial community.In this study,three types of forests,including pure bamboo forest,expanded forest and subtropical secondary evergreen broad-leaved forest,were selected in Miaoshanwu Nature Reserve,Zhejiang Province,China.The phospholipid fatty acid（PLFA）and high-throughput sequencing were used to investigate the composition of soil microbes and rhizosphere microorganisms of dominant tree species,and microbial functions involved in the biogeochemical related were predicted by FAPROTAX and Fun Guild.The possible mechanism of bamboo expansion was discussed from the effects of expansion on the structure and function of microbial community in order to provide reference for bamboo management.The main conclusions in this paper are as follows:Soil pH significantly increased while SOC and C/N decreased after bamboo expension;soil TN,TP,C_mic and N_mic content did not change significantly.Bamboo expansion can change the physical and chemical properties of the soil to some extent.Bamboo expansion did not significantly affect the PLFA composition of soil.The main changes in the five PLFAs,15:0 iso,16:0,16:0 10-methyl,18:0 10-methyl and 18:1 w7c,led to alteration in soil microbial community structure at the PLFA level.The content of arbuscular mycorrhizal fungi significantly increased,but decrease occurred at the ratio of 17:0 cyclo/18:1w7c and 19:0 cyclo/18:1w7c,which are employed to indicate the microbial community by soil nutrient and physiological stress,and the ratio of Gram-positive bacteria/Gram-negative bacteria slightly decreased.The result showed that the expansion of bamboo increased the competitiveness of soil nutrients by increasing arbuscular mycorrhizal content.Soil physicochemical properties showed good correlation with many indicators of soil microbial community,indicating that the change of soil physicochemical properties was the main reason for the change of soil microbial community structure after bamboo expansion.The expansion of bamboo caused a significant increase in the total number of species in the rhizosphere,but had no significant effect on community diversity of rhizosphere of Cyclobalanopsis glauca.There was no effect on the total number of species and species diversity of rhizosphere bacteria of moso bamboo.After bamboo expansion,the rhizosphere bacterial community structure of Cyclobalanopsis glauca changed significantly and gradually resembled that of moso bamboo.The change showed that the percentage of Proteobacteria,Actinobacteria and Cyanobacteria decreased significantly,the percentage of Acidobacteria was significantly increased,and the bacterial gate level in the rhizosphere of moso bamboo was not significantly changed.This indicated that the zonal dominant species community could adjust their response strategies to rhizosphere microorganisms under the stress of externa competitors.Meanwhile,the relative content of Nitrososphaera,Singulisphaera and other bacteria related to nitrogen cycle in the rhizosphere of Cyclobalanopsis glauca was significantly reduced after the expansion of bamboo,which may be one of the reasons to the growth of zonal tree species slowed down.Bamboo expansion had no significant effect on the total number of species and community diversity of Cyclobalanopsis glauca fungi,however the species diversity of moso bamboo rhizosphere fungi was drastically.The expansion of bamboo has effect on the community structure of rhizosphere fungi in Cyclobalanopsis glauca.After expansion,the percentage of Ascomycetes decreased and Zygomycota increased significantly in rhizosphere of Cyclobalanopsis glauca,and the percentage of Basidiomycota in rhizosphere of moso bamboo increased significantly.The fungal community structure in rhizosphere of Cyclobalanopsis glauca was similar to moso bamboo.The expansion of bamboo resulted in a significant decrease in the relative content of symbiotic in the rhizosphere of Cyclobalanopsis glauca,and a significant increase in the relative content of pathogenic.And there was no significant change in the trophic modes of rhizosphere fungi.It means that the ability of zonal dominant species to withstand drought or pests and other external stresses will be reduced after expansion of bamboo,which will be unfavorable to the healthy development of zonal forests.In conclusion,this study shows that the expansion of bamboo resulted in significant changes in soil microbial community structure and related functions.On the one hand,bamboo increased its competitiveness in soil nutrient acquisition by increasing the number of arbuscular mycorrhizal fungi.On the other hand,bamboo reduced the relative content of bacteria associated with nutrient（nitrogen）uptake and the symbiotic fungi related to disease resistance and drought in rhizosphere of zonal dominant trees,which can weaken competitors’ability to obtain nutrients and even their viability.These findings would explain the impact of bamboo expansion on forest ecosystem regeneration or growth from the ground level in the previous reports.