Effects Of Thinning Intensity On Soil Active Organic Carbon In Pinus Massoniana Plantation

Taking a 29-year-old Pinus massoniana Plantation at Lishui Forest Farm in Nanjing which was imposed lighit(LIT,25%),moderate(MIT,45%),high(HIT,65%) thinning intensity and a control chek(CK,0%) as the object,this paper studied the effects of different thinning intensities on the content of total organic carbon(TOC), active organic carbon( microbial biomass carbon(M-BC), particulate organic carbon(POC), light fraction organic carbon(LFOC), readily oxidized carbon(ROC),dissolved organic carbon(DOC),and neutral sugar(NS)) and the distribution proportion of active oraganic carbon in the total organic carbon in the surface(0~10cm) and subsurface soil(10~20cm).The results showed that:(1) The content of soil total organic carbon and active organic carbon show a law of diminishing along soil depth. Differences among different thinning intensities were found for total organic carbon and active organic carbon and the differences differed with soil depth. Compared with the CK,MIT significantly(P<0.05) increased the content of TOC to 110.1 % in surface soil. HIT significantly decreased the contentof TOC to 73.73 % in subsurface soil.LIT and HIT significantly decreased the content of MBC to 90.81% and 85.98% respectively both in surface and subsurface soil. MITsignificantly increased the the content of MBC to 108.3 %in subsurface soil. HIT significantly increased the content of POC to 105.5 % in surface soil.LIT and MIT significantly increased the content of POC to 129.4% and 108.2% respectively in subsurface soil. LIT,MITand HIT significantly decreaed the content of LFOC to 68.93 %,57.02% and 72.72% respectively both in surface and subsurface soil.MIT significantly increased the content of ROC to108.0% in surface soil. HITsignificantly decreased the content of ROC to 82.93%. LIT and MIT significantly increased the content of DOC to113.4% and 115.3% respectively both in surface and subsurface soil. LIT and HIT significantly decreased the content of NS to 86.68% and70.34% respectively both in surface and subsurface soil. MIT significantly increased the content of NS to 118.8% in subsurface soil.(2) The distribution proportion of MBC,POC,LFOC,ROC,DOC and NS in the TOC in soil(0~20cm) ranged from 1.75% to 3.10%, from 36.36% to 57.96%, from 14.70% to 30.20%, from 3.91% to 4.75%, from 0.06% to 0.10%, and from 13.53% to 18.67% respectively. Compared with the CK, LIT decreased the distribution proportion of MBC, LFOC,NS in the TOC and increased the distribution proportion of POC,ROC, DOC in the TOC respectively. MIT decreased the distribution proportion of POC, LFOC, ROC,NS in the TOC and increased the distribution proportion of MBC, DOC in the TOC respectively. HIT decreased the distribution proportion of LFOC, NS in the TOC and increased the distribution proportion of MBC,POC,ROC, DOC in the TOC respectively.(3) Soil active carbon was significantly positively correlated(P<0.01) or positively correlated(P<0.05) with soil total organic carbon. MBC,LFOC,ROC, DOC were significantly positively correlated with soil water content. MBC, ROC, DOC were significantly positively correlated with soil temperature and POC was significantly negatively correlated with soil temperature. DOC was significantly negatively correlated with p H. Excluding the NS, the correlation between all the other soil active carbon and the ratio of soil total organic carbon to total nitrogen was significantly positive. LFOC,ROC were significantly positive with the ratio of microbial biomass carbon to microbial biomass nitrogen and NS was significantly negatively correlated with the ratio of microbial biomass carbon to microbial biomass nitrogen.Among soil active carbon, ROC, DOC were significantly positively correlated with MBC and the correlation s were the lagest. POC was significantly positively correlated with LFOC and the correlation was the lagest. NS was only correlated with MBC, showed a negative correlation.