Effects Of Thinning On Soil Active Organic Carbon In Pine-oak Mixed Forest In The Qinling Mountains

Soil organic carbon(SOC) is one of main components in soil nutrients and its decomposition dynamics plays a vital role in the global carbon cycling. The labile soil organic carbon(LOC) is known as the active chemical component and the sensitive indicators of soil organic carbon dynamics which is generally characterized by dissolved organic carbon(DOC) and microbial biomass carbon(MBC), etc. Among them, DOC as energy substances of soil microbial activities, it promotes soil biochemical conversion processes and affects change of soil nutrients significantly. Although MBC has an insignificant proportion in SOC, its quick turnover time makes it extremely important in soil fertility and plant nutrition. To explore the effects of forest thinning on LOC, dynamics of soil organic carbon decomposition and seasonal dynamics of LOC, the quadratic general rotary design was applied in a pine-oak mixed forest thinning experiment in the middle Qinling Mountains with two control factors, thinning intensity(TI) and thinning residue removed rate(TR). Based on field sampling and laboratory analyzing, traits of LOC, decomposition dynamics of SOC and seasonal dynamics of LOC were analyzed. The main findings were follows.1. The content of LOC decreased in soil profile; soil water dissolved organic carbon is restricted by TI in the depth of 0~10cm soil;MBC was restricted by TR in the depth of 10~20cm soil.2. The rate of soil organic carbon decomposition was quicker at beginning period of incubation; the LOC and slow active organic carbon turnover was fastest as TI was 22.07% and TR was 85.36% in depth of 0~10cm soil; soil active carbon turnover was fastest as TI was 7.93% and TR was 14.64% in depth of 10~20cm soil; soil slow carbon turnover was fastest as TI was 22.07% and TR was 85.36%.3. The content of total organic carbon was most in the spring and the least in autumn; the content of microbial biomass carbon was the most in spring, less in summer and autumn; the content of DOC was the most in summer and less in spring and autumn.4. The optimal combination of tending measure was TI ranging from 16.34% to 17.05%, TR ranging from 35.86% to 40.69%, under the condition, the content of LOC and soil available nutrients were most, and decomposition rate of SOC was least.