The Effect Of Mountain Closure On Soil C-N-P Stoichiometry In Subtropical Natural Secondary Forests

Soil is not only an important place for material and energy exchange in terrestrial ecosystem,but also a product of the interaction between biological and inorganic environment.To understand the impacts of the long-term restoration of the subtropical degraded natural secondary forest restoration on soil physical and chemical properties,we employed a chronosequence to examine the responses of soil nutrient and C-N-P stoichiometry at 3 different levers of the soil(0-10 cm,10-20 cm and 20-30cm)over time(0 to 35 years)since the cessation of anthropogenic disturbances in two succession processs(Conifer-Broadleaf and Broadleaf-Broadleaf)and used old forests as a reference in subtropical Southeast China.Each of stage succession set up five age sequence: 0 years(no fencing,continuous collection of fuel wood and grazing,no measures of mountain closure for forest cultivation),3-6 years,11-12 years,21-24 years,31-35 years,and old forest with no human disturbance in history(time greater than 100 years)was selected as the reference.Main study conclusions as follows:(1)Soil pH and bulk density significantly reduced and the soil water content was significantly increased via the natural ecological restoration measures of mountain closure in the two succession processs.(2)Soil C and N concentrations increase with time since restorationin in the two succession processs,and the nitrogen content was closer to that of the old forest.However,the soil phosphorus decreased with time and was the lowest in the old forest.(3)The C:N ratio decreased with time,while C:P and N:P ratio increased over time since restorationin in the two succession processs.(4)Soil pH,water content and bulk density played a certain role in the formation of soil total C,total N and total P concentrations and the influence of C:N,C:P and N:P ratios.The above result suggested long-term ecological restoration may enhance the concentrations of soil total carbon,total nitrogen,and soil carbon: phosphorus and nitrogen: phosphorus ratios,whereas the concentrations of soil total phosphorus and the carbon: nitrogen ratio decreased weakly with the restoration of vegetation.This is due to the cumulative input of litter and root turnover after the cessation of disturbance,as well as plant absorbed nutrients from the soil to increase itself biomass.In addition,our study indicated that the nitrogen limitation decreased with time and the phosphorus limitation increased with stand development after the restoration in the two succession processs.The phosphorus limitation is weaken to old forest was closer in the later stage of ecological restoration than in the earlier stage in the two succession processs.Additional insights were offered toward the sustained stewardship of forests,while further guidance was given for the restoration of hillside ecosystems in Southeastern China,which can be applied to similar sites under comparable environmental conditions.