Soil Labile Nitrogen Pool And Nitrogen Transformation Of Degraded Subtropical Forests After Close-to-nature Transformation In The Initial Stage

The close-to-nature transformation management system which aims at multi-functional forest provides a feasible model for scientific forest management and sustainable development of multiple benefits.It emphasizes to adapt nature laws to ensure the stability of ecosystem,carrying out gradual transformation and do not disturbing normal ecological processes as much as possible.In this paper,we studied the characteristics of soil labile nitrogen pool and nitrogen transformation in the initial stage of transformation to explore the changes of nitrogen cycling.Then evaluate the impact of ecosystem stability,and provide basic data and references for forest management.Our experiments located in the Tingxiahu forest farm?121.204 E,29.677 N?and the Yuwang forest farm?121.748 E,29.855 N?in Ningbo,Zhejiang Province.Through seasonal sampling,PVC in-situ incubation method and static box method,we studied the effect of the main components of soil labile nitrogen pool,soil mineralization rate and soil N₂O emission flux.The main findings are as follows:?1?The contents of soil dissolved organic nitrogen?DON?,microbial biomass nitrogen?MBN?,ammonium nitrogen?NH₄⁺-N?and nitrate nitrogen?NO₃^--N?were not significantly changed compare to control plots in the initial stage after close-to-nature transformation of 0¹0 cm soil layer,but the MBN content increased by 17.05%and5.92%,the DON content decreased by 18.25%and 8.91%,the NH₄⁺-N content decreased by 21.72%and 26.26%of Tingxiahu plots and Yuwang plots,respectively.?2?There were no significant differences in soil net mineralization rate,net ammoniation rate and net nitrification rate between transformation and control plots over one year.However,the average net mineralization rate,average net ammoniation rate and average net nitrification rate of transformation plots increased by 0.12 mg·kg·d^-1,0.09 mg·kg·d^-1 and 0.01 mg·kg·d^-1 of Tingxiahu plots.In Yuwang plots,the average net mineralization rate and the average net ammoniation rate decreased by 0.02mg·kg·d^-1 and 0.36 mg·kg·d^-1,respectively.The average net nitrification rate increased by 0.11 mg·kg·d^-1.?3?Soil N₂O flux in the rapid growth season did not change significantly compared to control plots over one year.However,the transformation plots of Tingxiahu and Yuwang increased by 68.58%and 17.66%,respectively,compared to control plots.In summary,after close-to-nature transformation,the activity of soil labile nitrogen pool and nitrogen circulation increased to some extent,but there shows no significant difference between two treatments.It indicates that after close-to-nature transformation,degraded forests can basically maintain the original nitrogen cycling process,thus achieving the goal of sustain stability through close-to-nature transformation.