Seasonal Dynamics Of Soil Microbial Communities Under Different Forest Types In The Xinjiashan Forest Region Of Qinling Mountains

Microorganism is an important part of forest ecosystem,which is one of the important driving forces of the earthbiochemical cycle.Soil microbes participate in carbon and nitrogen cycling,and provide effective nutrient for plant growth.However,little is known about the responses of microbes participateto the seasonal changes.In this study,the bacterial composition during four seasons and at four soil depths(0–10,10–20,20–40 and 40–60 cm)in three forests(Piceaasperata Mast.;Betulaalbosinensis and shrub forest)of the Qinling Mountains was investigated.Illumina 16 S rRNA gene sequencing was used to analyse soil microbial diversity and communities.The soil properties,including soil pH,soil temperature,soil water content,soil organic carbon,soil active organic carbon(dissolved organic carbon,microbial biomass carbon,easily oxidized organic carbon),soil enzyme activities(?-1,4-xylosidase,?-1,4-glucosidase,cellobiohydrolase,?-N-acetylglucosaminidase)were determined.The main results were as follows:(1)Soil organic carbon content showed significant among different forest types in different seasons.The soil organic carbon,dissolved organic carbon,easily oxidized organic carbon,and microbial biomass carbon content were highest in Betulaalbosinensis.The soil organic carbon,dissolved organic carbon,easily oxidized organic carbon,and microbial biomass carbon content decrease with the increase of soil depth and showed significant seasonal variation.The soil organiccarbon,dissolved organic carbon,easily oxidized organic carbon,and microbial biomass carbon contents reached their maximumin autumn,and reached their minimumin winter.The correlation analysis showed that dissolved organic carbon,easily oxidized organic carbon,and microbial biomass carbonare significantly related with soil organic carbon,soil temperature,and soil water content.(2)Soil enzyme activities showed significant spatial and temporal variability.The activities of?-1,4-xylosidase and?-1,4-glucosidase were highest in Betulaalbosinensis,whereascellobiohydrolaseand?-N-acetylglucosaminidase were highest in Piceaasperata Mast.The activities of ?-1,4-xylosidase,?-1,4-glucosidase,cellobiohydrolase and?-N-acetylglucosaminidase in all type of forests decreased as the soil gets deeperand showed significant seasonal variation.The four soil enzymes activities in summer and autumn were higher than in winter and spring.Soil enzyme activities had significant correlation with dissolved organic carbon,easily oxidized organic carbon,microbial biomass carbon,soil organic carbon,soil temperature,and soil water content.(3)The Chao1 richness and Shannon diversity indices of soil bacteria at the four depths typically decreased from warm summer to cold winter,correlated with the decrease in soil temperature.The bacterial community was significantly affected by seasonality in all forests.Phyla Acidobacteria,Bacteroidetes and Proteobacteria were dominant bacterial communities throughout the soil profile.Overall,soil bacterial communities generally changed from Acidobacteria-dominant in summer to Bacteroidetes-dominant in winter.Soil dissolved organic carbon,easily oxidized organic carbon,microbial biomass carbon,soil organic carbon,soil temperature,soil water content,?-1,4-xylosidase,cellobiohydrolase,?-1,4-glucosidase,and?-N-acetylglucosaminidase had significant correlation with soil bacterial communities.Redundancy analysis(RDA)showed that soil pHandsoil temperature are the most important factors shaping the microbial communities.(4)The Chao1 richness and Shannon diversity indices of soil fungi at the four depths typically decreased from warm summer to cold winterin all three types of forests,which was probably due to the decrease in soil temperature.Phyla Basidiomycota and Ascomycota were dominant fungal communities throughout the soil profile.The Basidiomycota abundance decreased with the increase of soil depth,while the abundance of Ascomycotaincreased with the increase of soil depth.The fungal communitiy was significantly affected by seasonality in all types of forests.The abundance of Basidiomycota increased with soil temperature increase,whereas the abundance of Ascomycota decreased as temperatureincreasing.Correlation analysis showed that soil bacterial communities had significant correlation with dissolved organic carbon,easily oxidized organic carbon,microbial biomass carbon,soil organic carbon,soil temperature,soil water content,?-1,4-xylosidase,cellobiohydrolase,?-1,4-glucosidase,and?-N-acetylglucosaminidase.Redundancy analysis(RDA)results showed that soil temperature was the first primary factor for the variation of fungal communities.The results of this study showed that seasonal changes of microbial not only influenced by soil nutrient,but also affected by environmental factors.Thus,soil temperature represents important factor contributing to the observed microorganism variations.