| The mountainous and hilly areas in the south and the upper and middle reaches of the Yangtze River are the core and key areas of my country’s ecological restoration and protection,and are an important part of my country’s"two screens and three belts"ecological security construction.However,unreasonable development and utilization have led to weak ecosystem service capabilities in the region,which are prominently manifested in ecological problems such as serious soil nutrient loss,reduced biodiversity,and decreased water conservation capabilities.Taking the secondary forest of Cyclobalanopsis glauca after two years of thinning in Tianxinge Forest Farm in the hilly area of western Hunan Province as the research object,four kinds of thinning intensity（50%,HIT;30%,MIT;15%,LIT;0%,CK）of the secondary forest of Cyclobalanopsis glauca were studied.The three soil layers of 0-10cm,10-20cm,and 20-30cm,through field sampling and indoor experiment analysis,study the content of soil organic carbon and its active components（soil microbial biomass carbon（MBC）,particulate matter）under different thinning intensities.Organic carbon（POC）,soil soluble organic carbon（DOC）and easily oxidizable organic carbon（ROC）)and distribution ratios,as well as changes in soil nutrients,to explore the effect of thinning on the soil carbon management index（CMI）and soil carbon storage（SOCs）)Distribution influence,in practice,according to different forest management goals,determine the most suitable thinning intensity,and provide decision-making basis for forest scientific management.The result shows:（1）Thinning treatment significantly changed the soil physical and chemical properties（soil moisture content,bulk density,p H）and soil nutrient indexes（total organic carbon,total nitrogen,available nitrogen,total phosphorus,total potassium）of the secondary forest of Cyclobalanopsis glauca（P<0.05）).The content of soil moisture,bulk density,p H,organic carbon,total nitrogen,and alkali-hydrolyzable nitrogen showed HIT>MIT>LIT under different thinning,and soil total phosphorus and total potassium showed LIT>MIT>HIT under different thinning.Soil C/N and C/P showed MIT>HIT>LIT,and N/P showed HIT>MIT>LIT,but the difference of soil C/N,C/P,N/P under MIT and HIT treatments was not significant.Under different thinning intensities,soil nutrients are mainly concentrated in the surface soil,and the content decreases as the soil layer deepens.HIT treatment is most conducive to the improvement of various indicators.（2）Thinning changed the content and distribution ratio of soil active organic carbon in the secondary forest of Cyclobalanopsis glauca.The content of soil organic carbon（TOC）,soil microbial biomass carbon（MBC）,soluble organic carbon（DOC）,particulate organic carbon（POC）and easily oxidizable organic carbon（ROC）are respectively 11.41～39.96 g·kg-1,Between35.02～137.48 mg·kg-1,79.93～239.21 mg·kg-1,2.51～16.22 g·kg-1 and 0.85～7.62 g·kg-1.As the intensity of thinning increases,the soil organic carbon content（TOC）,soil microbial biomass carbon（MBC）,particulate organic carbon（POC）and easily oxidizable organic carbon（ROC）are shown as HIT>MIT>LIT（P<0.05）,the soil soluble organic carbon（DOC）decreased with the increase of thinning intensity,which showed that LIT>MIT>HIT（P<0.05）.Thinning changes the distribution ratio of soil active organic carbon components.Under moderate thinning,the proportion of soil particulate organic carbon（POC）,easily oxidizable organic carbon（ROC）and microbial biomass carbon（MBC）in total soil organic carbon increased;compared to MIT,HIT increased soil soil particulate organic carbon The distribution ratio of（POC）and microbial biomass carbon（MBC）reduces the distribution ratio of easily oxidizable organic carbon（ROC）;thinning reduces the distribution ratio of soluble organic carbon（DOC）（P<0.05）.Therefore,the content of active organic carbon increased under HIT treatment,and it is also more conducive to the stability of the soil carbon pool.（3）The soil carbon management index（CMI）and soil carbon storage（SOCs）of the secondary forest of Cyclobalanopsis glauca increased with the increase of thinning intensity（P<0.05）.Compared with the control plot,the soil carbon stock management index（CMI）under the HIT,MIT,and LIT treatments were 1.65 times,1.63 times,and 1.05 times that of the CK treatment,respectively;the soil carbon storage（SOCs）under the HIT and MIT treatments were respectively higher than that of the CK treatment.Treatments increased by 18.94%and 21.54%（P<0.05）.Compared with CK treatment,LIT treatment decreased by 3.49%（P>0.05）;HIT thinning not only improved soil carbon accumulation capacity but also increased the stability of carbon pool.Promote the improvement of soil quality.（4）There is a certain correlation between soil active organic carbon and soil nutrients,soil properties and soil carbon pool management index,and there is a certain mutual transformation between active organic carbon components.Soil microbial biomass carbon（MBC）,particulate organic carbon（POC）,easily oxidizable organic carbon（ROC）and soluble organic carbon（DOC）are extremely significantly positively correlated with soil total organic carbon and soil total nitrogen content（P<0.01）,Soil microbial biomass carbon（MBC）,particulate organic carbon（POC）and easily oxidizable organic carbon（ROC）are significantly or extremely significantly positively correlated with soil water content and soil C/N（P<0.05,P<0.01）.Microbial biomass carbon（MBC）,easily oxidizable organic carbon（ROC）and soluble organic carbon（DOC）have a negative correlation with soil p H and soil bulk density.Soil microbial biomass carbon（MBC）,particulate organic carbon（POC）and easily oxidizable organic carbon（ROC）are significantly positively correlated with soil carbon pool activity index（P<0.05）,soil microbial biomass carbon（MBC）,particulate organic carbon（POC）,easily oxidizable organic carbon（ROC）,and soluble organic carbon（DOC）are significantly positively correlated with soil carbon stock management index（CMI）and soil carbon storage（SOCs）（P<0.01）. |
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