Effects Of Nitrogen Deposition On Soil Organic Carbon And Microbial Properties In Evergreen Broad-leaved Forests Of Subtropics

The effects of nitrogen deposition on organic carbon in forest ecosystems are currently one of the hot spots in ecological research.Microbial As an important driver in the soil nutrient cycling process,play a very important role in the process of organic carbon cycle.Previously because of research technology Limitations,the understanding of the structure and function of soil microbial communities are not deep enough,the development of high-throughput sequencing technology provides us an opportunity to further study the soil organic carbon and microbial characteristics.The sample plots were selected in a natural evergreen broad-leaved forest in the Nature Reserve of Castanopsis kawakamii in Sanming City,Fujian Province,treatment included control(CT,0 kgN ha-1 a-1),low nitrogen(LN,40 kgN ha-1 a-1)and high nitrogen(HN,80 kgN ha-1,a-1).The samples of 0-10 cm soil layer were taken January and July 2017 respectively to determine the soil physical and chemical characteristics and organic carbon content.The 16S rDNA sequencing technology and PICRUSt gene function prediction were used to analyze the response of soil microbial species and function to nitrogen deposition.The situation reveals the microbial mechanism of nitrogen deposition affecting soil organic carbon in evergreen broad-leaved forests of mid-subtropical China.The main result is the following:a.Soil total organic carbon(SOC)content was not significantly affected by nitrogen deposition treatment,but nitrogen addition significantly promoted the accumulation of soluble organic carbon(DOC)in summer,and the DOC content of each treatment in summer was significantly higher than that of winter,which increased about one time.b.Under the influence of nitrogen deposition,microbial biomass carbon(MBC),nitrogen(MBN),and phosphorus(MBP)in winter were significantly reduced about 20%,22%,and 44%in high nitrogen treatment.And low nitrogen and high in summer,the microbial biomass significantly decreased,the decline was greater than in winter.c.Alpha diversity of soil microbial communities decreased significantly during winter in high nitrogen treatments,with no differences between treatments in summer.Nitrogen deposition had no significant effect on soil microbial community structure,but it had a significant effect on the relative abundance of some susceptible bacterial.In contrast,nitrogen deposition has a greater impact on the function of soil microbial communities,with significant functions including reduced degradation of recalcitrant carbon,faster metabolism of nutrients,accelerated translation,and increased energy metabolism.d.The main environmental factors affecting the changes of soil microbial community structure and function by nitrogen deposition are the soil available nutrient contents.Among them,DOC and NH4+-N are the main factors affecting the microbial community structure in winter,and MBN in summer.The winter seasons affecting the functions of microbial communities are mainly NO3--N and MBN,MBC and MBN in summer.