Characteristics Of Nitrogen And Phosphorus Availability Along Restoration Ages Of Pinus Massoniana Plantations In Red Soils Erosion Regions At Southern China

Vegetation restoration is one of the most important measures to control soil erosion.Hilly red soil regions of southern China is the second largest soil erosion area in China after the Loess Plateau,so a great deal of researches have been carried out on the effects of vegetation restoration on soil nutrient content in this region.However,the transformation,supply and depletion mechanism of nitrogen（N）and phosphorus（P）nutrient availability is still not clear.N,P is the most universal and important limiting factor of soil nutrient in forest ecosystem,thus it is of great significance to find out the seasonal variation of soil nitrogen and phosphorus nutrient availability for the study and evaluation of vegetation restoration and reconstruction in the red soil erosion area of southern China.In this study,the forest land（bare land,10 years,20 years,30 years old Pinus massoniana plantation and natural secondary forest）in different vegetation restoration stages in the hilly red soil erosion area of southern China was taken as the research object.The research contents are as follows:（1）soil and leaf C,N,P contents and ecological stoichiometric characteristics of forest land in different vegetation restoration stages;（2）seasonal dynamic effects of vegetation restoration on soil N and P nutrient availability;（3）dynamic characteristics of soil N,P nutrient leaching loss and gaseous N emission loss in different vegetation restoration stages.The main findings are as follows:（1）During the restoration of Pinus massoniana plantation,the C and N nutrients in the surface layer（0-10 cm）soil increased obviously,while the C and N nutrients in the deep layer（>10 cm）soil did not increase significantly.At the same time,the soil P nutrient in each soil layer did not increase obviously.There was a significant positive correlation between soil and plant leaf C,N and P nutrients.In addition,compared with the zonal natural secondary forest,the soil N and P nutrient content of Pinus massoniana plantation in different restoration ages were still significantly lower than that of the natural secondary forest.The imbalance of ecological stoichiometric ratio of soil and leaf C:N:P indicates that with the gadual restoration of vegetation in the eroded area of red soil in southern China,the partial restriction of soil N nutrient may be relieved gradually,while the P nutrient restriction will be further aggravated.（2）The contents of NH₄⁺-N,NO₃^--N,available N,DON,available P and MBC,MBN did not increase significantly in the vegetation restoration process,and compared with the zonal natural secondary forest,there was still a significant difference between the soil NH₄⁺-N,NO₃^--N,available N,DON,available P and MBC,MBN.The soil net mineralization rate was mainly shown as the rate of net ammoniation,the nitrification of soil was weak,and the available N pool of soil was mainly NH₄⁺-N,the content of NO₃^--N was low,and the supply mechanism of soil available N was unstable.There was a significant positive correlation between soil MBC,MBN and inorganic N components,DON and available P,which could well indicate the change of soil nutrients during vegetation restoration.（3）Soil inorganic N leaching was mainly in the form of soil NH₄⁺-N in forest land at different vegetation restoration stages,while NO₃^--N was the main form in natural forest.With the increase of vegetation restoration years,the contents of NH₄⁺-N and NO₃^--N in soil leaching solution were not controlled obviously.N₂O in forest soil was mainly absorbed by different vegetation restoration stages,and N₂O emission rate was positively correlated with soil net nitrification,net ammoniation and net mineralization rate.The N₂O absorption of various forest soils showed an increasing trend with the increase of recovery years.In the future,it is of great importance to continue to strengthen the restoration and control of vegetation in soil and water erosion areas,minimize the damage caused by man-made factors to the ecological environment in soil and water erosion areas,and meanwhile apply soil N and P fertilizer appropriately,so in order to gradually enhance the function of forest vegetation conservation in water and fertilizer conservation in forest areas.Ultimately,speeding up the promotion of soil improvement and vegetation restoration efficiency as well as improving the overall service function of forest ecosystems.