Effects Of Precipitation Reduction And Nitrogen Addition On Soil Organic Carbon Content And Soil Microbial Community In Subtropical Mountain Forests

Changes of precipitation pattern and nitrogen deposition are major aspects of global change,and can regulate the terrestrial carbon cycling significantly.The humid mid-subtropical forests,which account for 10% of the total forest area in the world,are characterized as having high species diversity and high productivity.Both the vegetation and the soil in this forest store huge carbon sources.According to the nearest IPCC report,the amount of precipitation might decrease and nitrogen deposition might intensify in the mid-subtropical area.Understanding how soil carbon cycling will response to reduced precipitation and nitrogen deposition in the mid-subtropical forests are therefore important to the accurate estimation of carbon budget in future global change.In this study,an field simulation experiment(precipitation reduction and nitrogen addition)was conducted in three catchments in the Badagongshan Mountain in midsubtropical zone of China.The content and composition of soil organic carbon(SOC)were detected to assess how would these variables will response to precipitation reduction and nitrogen addition.The soil enzyme activities,microbial community(PLFAs)and community-level physiological profiling(Biolog method)were detected to assess the microbial roles in soil carbon cycling.Through this study,we'll gain a better understanding in how soil organic carbon pool in mid-subtropical forest may respond to future global change.The following main conclusions were drawn:(1)The basic physical and chemical properties of the soil are stable under the precipitation reduction and nitrogen addition.(2)Neither the precipitation reduction nor nitrogen application had significant effect on the content of SOC,TN,DOC and POC,and no interaction effects were found.Nitrogen addition didn't increase the contents of soil ammonium-N and nitrate-N.(3)The activity of glucosidase decreased with the increase of nitrogen application.The hydrolase activity decreased with the increase of nitrogen application.In the 2/3 precipitation reduction treatment,and in the no precipitation reduction and 1/3 precipitation reduction treatments the enzyme activity reached its maximum in the high nitrogen addition treatment in the 0-10 cm soil.Soil enzyme activities were significantly affected by the content of SOC,TN and other nutrients.(4)Precipitation reduction and nitrogen addition did not significantly affect the composition of soil microbial community,nor did they significantly affect the s microbial substrate utilization pattern.In this study,soil physicochemical properties and SOC content composition were not affected by precipitation reduction and nitrogen application,for the following reasons: firstly,the field test was short and the soil spatial heterogeneity was large;secondly,there was abundant precipitation in the region and water was not the limiting factor,so the effect of precipitation reduction was weak;thirdly,due to abundant precipitation,the added nitrogen was easily lost by leaching,thus weakening the effect of nitrogen addition.However,the microbial community composition and the ability of microbial carbon source utilization have not changed significantly yet,and the effect on soil carbon cycle may become more pronounced with the prolongation of treatment time.