Effect Of Thinning Intensity On Soil Carbon Sink In Korean Pine Dominated Over-cut Forest In The West Of Changbai Mountain

Overcut natural forest, the main kind of secondary forest in Northeast China, are capable of recover to high-quality Korean pine-broadleaved forest, with the artificial induction. However, stand soil carbon sink, ability and its response to forest thinning have not been well characterized. This study was conducted in Changbai Mountain. In this region, three thinning density(Heavy(HIT), Low (LIT) and reference) were used to the overcut forest, after5years recovery, stands soil carbon storage, labile organic carbon content, carbon density in litter layer, decomposition rates and soil respiration were determined, in order to investigate effects of thinning intensity on carbon sink and reveal mechanism how thinning affects soil carbon storage. Results showed that:HIT could increase the soil carbon content (0-20cm layer) and total storage. Thinning, especially LIT could improve the content of microbial biomass carbon, water-soluble organic carbon and readily oxidation carbon and their availability of soil labile organic carbon and activity of carbon pool. Soil carbon content (0-10cm,10-20cm layers) increased with the thinning intensity, particularly in the top layer (0-1Ocm), in which carbon content in the HIT and LIT were62%and52%higher than the control(p<0.05). Three kinds of soil labile organic carbon content upon thinning treatments were higher than control. Availability of soil labile organic carbon and activity of carbon pool were highest upon LIT.Thinning may be disadvantage for the litter accumulation and carbon storage. Litter content declined with thinning density, HIT (4.67t·hm-2) were significantly lower than the control (7.81t·hm-2) and LIT (7.05t·hm-2)(p<0.05), but the latter two treatments were not significantly different with each other(p>0.05). Carbon density in litter layer were also decreased with thinning densityThinning increased the decomposition rate of litter and LIT accelerated the decomposition of litter and the release of carbon. Decomposition coefficient K of HLT and LIT (0.782and0.715, respectively) were higher than control, t0.95(3.831a, and4.190a, respectively) were lower than control. Carbon released quantity and rates were highest in the LIT.HIT could decrease soil respiration. Soil respiration rates of all seasons were lowest in LIT. Soil temperature in5cm showed greater influence on soil respiration than the temperature in10cm, Q10. the temperature sensitivity index of soil respiration, were highest in the control stands.Taken altogether, thinning increased the rate of soil carbon import by improving litter decomposition rate and decreased soil carbon export by reducing soil respiration rate, resulting in increased soil carbon storage. In addition, although LIT also accelerated litter decomposition and had higher soil carbon release, but its soil carbon storage was still lower than that of HIT, indicating that in this research, thinning influenced soil storage mainly via regulating soil respiration rate.