Effects Of Restoration Of Massoniana-Dicranopteris Community On Nitrogen Cycling In Red Soil Erosion Area

Nitrogen is one of the important nutrient elements needed for plant growth and development.The availability of nitrogen not only has a feedback relationship with community succession,and it is an important key factor limiting the productivity of forest ecosystems.Therefore,the study of the nitrogen cycle process plays an important role in evaluating the stability of ecosystems and ecological restoration.The sequence of vegetation restoration?Y0,Y16,Y34?was selected as the research object,and set three treatments:NRD?not removed D.dichotoma?,Rd?removed D.dichotoma?and CK?control?.In order to exploring the changes in the nitrogen cycle process and its impact mechanisms,the results show that:?1?Vegetation restoration had no significant effect on the nitrogen storage of NRD,but it increased the proportion of nitrogen pool allocation in tree layer,undergrowth vegetation layer and litter layer,and reduced the distribution ratio of nitrogen pool in soil layer.NRD increased the total nitrogen pool of Pinus massoniana ecosystem.In Y0,Y16and Y34,NRD increased the ecosystem nitrogen pool by 180%,28.01%and 56.45%,respectively.After removal of D.dichotoma,the nitrogen pool of?Y0?did not change significantly,while the nitrogen pools of Y16 and Y34 decreased significantly by 30.98%and 9.33%,respectively.It indicated that the contribution rate of nitrogen storage in vegetation layer to the nitrogen pool of Pinus massoniana ecosystem is increasing.At the same time,NRD was beneficial to the input of a large amount of nutrients into the soil and promoted the improvement of degraded red soil.?2?Vegetation restoration and NRD significantly increased the annual nitrogen return of erosion-degraded land.Compared with Y0,nitrogen return increased by 3.4times and 4.8 times,respectively,and CK increased by 6.8 times and 5.5 times,respectively.Meanwhile,NRD was 2.8 times,1.1 times and 2.3 times higher than CK in different recovery years.The annual return of total litter nitrogen in the community significantly affected the soil properties,and it was significantly negatively correlated with pH and NO₃^--N,and showed a significant positive correlation with TN,SOC,C/N,AP,DOC and DON.It also has a positive effect on soil enzyme activity,and has a significant or extremely significant positive correlation with AP,?G and NAG.It also exerts an important influence on the quantity and structure of soil microbial communities,and has a very significant positive correlation with MBC,MBN,GP,GN,ACT,Fungi,VAM and F/B,and has a significantly negative correlation with GP/GN.?3?The soil net nitrogen mineralization rate is negative in spring,rising in summer and autumn,and reaching a maximum in autumn,and then decreased in winter.NRD increases the net nitrogen mineralization rate of soil,which can provide more effective nitrogen for vegetation growth and development,and the net nitrogen mineralization rate decreases after removal of D.dichotoma.The increase in vegetation recovery years and the NRD can significantly increase the levels of TN,TP and DON,which in turn significantly increases the rate of nitrogen mineralization.Bacterial community is the main influencing factor of soil nitrogen mineralization process.Acidobacteria,Planctomycetes,Verrucomicrobia,and Thaumarchaeota promote the nitrogen mineralization rate and ammoniation rate.GAL15 inhibits it;GAL15 can significantly promote the nitrification process,while Bacteroidetes has an inhibitory effect.