Effects Of Thinning And Transform On Soil Respiration And Carbon Sequestration Capacity In Sprout Chinese Fir Plantation

Stand thinning and conversion of sprout forest could improve stand structure,and accordingly affect soil respiration,environmental factors and stand carbon storage inevitably.However,the systematic study is still scarce.The aim of this study is to compare the effects of different thinning intensity and suface organic matter treatments on soil respiration and related mechanisms and evaluate the effects of thinning on forest ecosystem carbon sequestration capacity in a Chinese fir plantation in subtropical China.The six treatments were carried out:(1)CKK:No thinning+keeping surface organic matter;(2)CKR:No thinning+removal of surface organic matter;(3)MTK:Moderate thinning(50%)+keeping surface organic matter;(4)MTR:Moderate thinning(50%)+removal of surface organic matter(5)HTK:Heavy thinning(70%)+keeping surface organic matter;(6)HTR:Heavy thinning g(70%)+removal of surface organic matter,respectively.The results showed:(1)The soil respiration(R_S)of moderate and heavy thinning increased by 11.3%and 24.4%,respectively,in the first year after thinning,and by 13.0%and 25.7%,respectively,in the second year after thinning,in comparison to the control.The soil respiration(R_S)of removal surface organic matter declined by 5.3%in the first year after thinning,and by 7.0%in the second year after thinning,in comparison to keeping surface organic matter;(2)Thinning intensity significantly affects soil respiration and soil temperature,and surface organic matter significantly affects soil respiration and soil organic carbon.The three types of soil active organic carbon components(MBC,WSOC and ROC)are very significantly related to the interaction between thinning intensity and surface organic matter(P<0.001).(3)T_S and ROC were the most critical factors affecting R_S,and soil labile organic carbon pools(sum of ROC,WSOC and MBC)even contributes more to soil respiration than soil temperature;(4)Compared with the beginning of thinning,the carbon storage of the tree layer in the control,moderate,and heavy thinning areas increased by 6.60,4.57 and 3.63 Mg·C·ha^-1,respectively,the soil carbon storage reduced by 3.95,0.06 and 0.27 Mg·C·ha^-1,which resulted in increase in forest carbon storage of 2.65,4.51 and 3.36 Mg·C·ha^-1 within 2 years of forest stand thinning and coversion;(5)Stand thinning and conversion may directly affect the concentration of soil organic carbon(SOC)and soil microclimate(T_S and M_S)through removal of trees and treating surface organic matter,and further stimulate the concentration of soil active organic carbon components(MBC,WSOC and ROC),which lead to increasing soil CO₂ flux.In summary,to increase the minimum soil CO₂ emission,improve forest carbon sequestration capacity,improve soil fertility and not reduce soil carbon storage under global climate change,medium thinning intensity and surface organic matter are preferred to convert the sprout Chinese fir plantations.