Effects Of Vegetation Types On Soil DOM Characteristics And Microbes In The Mid-subtropical Forests

In order to explore the relationship between soil DOM and microbial community and enzyme activity in different seasons and vegetation types in central subtropical regions.The 0-10 cm topsoil samples were sampled in November and April from the following 4 forests that were converted from natural Castanopsis kawakamii forest:the Natural secondary forest of Castanopsis carlesii(SF),Artificial-assisted natural regeneration forest of Castanopsis carlesii(AR),Plantation of Pinus massoniana(PM)and Chinese fir plantation(CF)in the conservation area located at mid-subtropical Field Station in Sanming,Fujian province.The physical and chemical properties,soil DOM contents,spectral structure,and microbial community structure and function of these samples were determined.Results showed that the season and vegetation types had significant effects on soil physicochemical properties,DOM quantities,spectral structures,microbial community structure and enzyme activities,the DOC content of all stands in April was higher than that in November,and the DON content in November was generally higher than in April.In the two quarters,the levels of DOC and DON in SF and AR were significantly higher than those in PM and CF.Infrared and three-dimensional fluorescence spectra showed that the total macromolecules and hard-to-decompose substances in the soil DOM were higher in each stand in April than in November.The PM and CF soils had more decomposed matter in the DOM than SF and AR.The growth rate of vegetation increased in April compared with that in November.The conversion rate of SOC to MBC was faster,and the MBC/MBN increased due to the increase of microbial biomass accumulation.The effect of N on enzyme activity was significant.DON is the main factor affecting soil enzyme activity.Broad-leaved forest soils contianed more easily decomposed of carbon,so the activity of PG and CBH was higher.On the contrary,the activities of PHO and PEO were higher in coniferous forest soils.In November,there were more GP in each stand,and there were more GN in April.In the two quarters,the order of F:B was SF>AR>CF>PM,which accords with the law of the stability of the ecosystem.During the growing season in April,the growth rate of vegetation accelerated,and nutrient consumption also accelerated.Therefore,all the forest stands were stressed by nutrients in April.The nutrient contents of PM and CF in conifer species are lower than those in SF and AR,so they are more severely affected by nutrient stress.In the two quarters,TN,DON and SOC were the key driving factors affecting soil enzyme activities in different forests.N dominated the region and played a leading role in nutrient utilization in the region.The C cycling enzymes and N cycling enzymes interacted with the soil carbon and nitrogen nutrients,and there was a certain coupling relationship between the carbon and nitrogen nutrient cycling.Fungi,GP and GN were the dominant mutant species in microbial communities in different seasons and different stands.SOC,MBC,MBN,NH4+-N,and NO3--N were the main driving factors for microbial community structure changes.Microorganisms have a certain selectivity for carbon utilization,and they tend to use easily decomposable organic carbon.The content of dissolved organic substances DOM has a significant effect on enzyme activity,but its quality have no significant effect on microbial community structure and enzyme activity.