Effects Of Different Improvement Treatments On Carbon Storage Of Pinus Massoniana Low-benefit Forest

Using Pinus massoniana low-benefit forest of different improvement treatments as the research object, this paper studied the effects which Replanting and Mixed(RM), Clearcutting and Reforestation(CR), Closing Mountains for Silviculture(CMS) exerted on organic carbon storage, soil labile organic carbon and soil carbon mineralization of Pinus massoniana low-benefit forest through the research methods as combination of field sampling, indoor determination and incubation experiment. Set the unimproved Pinus massoniana low-benefit forest as Control Check (CK). The results indicated that:(1) The organic carbon storage of the Pinus massoniana low-benefit forest plants layer of CR, CMS, RM showed the following results:RM had the maximum figure(50.18±5.55MgC·hm-2),0.42MgC·hm-2higher than CMS (49.76±2.35MgC·hm-2), significantly higher than CR(22.66±4.89MgC·hm-2) and CK (22.13±3.85MgC·hm-2)(P<0.05), respectively higher27.52MgC·hm-2and28.05MgC·hm-2. Organic carbon storage of Pinus massoniana low-benefit forest of CR, CMS, RM treatments followed the order of CR>CM>CMS, which were respectively higher47.81MgC·hm-2,16.53MgC·hm-2and13.29MgC·hm-2compared with CK. The organic carbon storage of the ecosystem of Pinus massoniana low-benefit forest of CR, CMS, RM all increased largely, and CR increased by48.34MgC·hm-2, were the largest, RM increased by44.58MgC-hm"2and CMS increased by40.92MgC·hm-2. This indicated that CR, CMS, RM all had some effects on improving carbon sequestration capacity of forest ecosystem after15years’Pinus massoniana low-benefit forest improvement, while CR were based on the principle of choosing the more appropriate trees to substitute Pinus massoniana, making forest ecosystem achieve the best carbon sequestration capacity.(2) Microbial biomass carbon (MBC) of the Pinus massoniana low-benefit forest of CR, CMS, RM followed the order of CR>CMS>CM, which respectively increased by142.29mgC·kg-1,69.82mgC·kg-1and16.81mgC·kg-1compared with CK, and any two of the three index were significantly different(P<0.05). Readily oxidation carbon(ROC), water-solubable organic carbon (WSOC) and mineralizable carbon(MC) of the Pinus massoniana low-benefit forest of CR, CMS, RM all followed the order of CR>CM> CMS, higher than CK. The soil labile organic carbon contents of CR, CMS, RM and CK decreased with the increase of soil depth. Ratio of soil labile organic carbon to TOC’s tendency followed the order of ROC>MC>MBC>WSOC. Ratio of soil labile organic carbon to TOC in CK were very high, and the ratio of ROC, MC were higher than that of CR, CMS, RM, respectively31.76%,3.73%; while the biggest soil labile organic carbon content in CR had lower ratio:the ratio of ROC, WSOC and MC in CR were the lowest, respectively19.95%、1.19%and2.61%. This indicates the SOC in Pinus massoniana low-benefit forest shows the weakest stability and was easily interfered by external environment to decompose and change; while the SOC in CR is the most stable and better for soil carbon fixation.(3) SOC mineralization rate of the Pinus massoniana low-benefit forest of CR, CMS, RM was between5.62mgC·kg-1·d-1～7.00mgC·kg-1·d-1after60days’ laboratory incubation at25℃, and the order was CR>RM>CMS, all higher than CK(P<0.05). SOC mineralization rate decreased with the increase of soil depth. The mineralization ratio of the Pinus massoniana low-benefit forest of CR, CMS, RM was between2.61%～3.73%, and the order was CK>RM>CMS>CR, CK was respectively2.75%,3.90%and42.91%higher than CM, CMS and CR. This indicated that the proportion of SOC’s mineralization to CO2of CK was the highest, which meant CK’s SOC showed the weakest stability and was easily interfered by external environment to decompose and change. Trends of soil carbon mineralization of CR, CMS, RM and CK were almost the same under the same incubation condition. The mineralization ratio of soil organic carbon was fast at the early stage and slow at the later stage.(4) The SOC and soil labile organic carbons of CR, CMS, RM and CK were significantly correlated positively(P<0.05) or highly correlated positively(P<0.01), which indicated that the contents of soil labile organic carbons of the Pinus massoniana low-benefit forest of CR, CMS, RM depended largely on the contents of TOC. Soil labile organic carbons of CR, CMS and RM were significantly correlated positively(P<0.05) or highly correlated positively(P<0.01), the soil labile organic carbons of CK were highly correlated positively(P<0.01). This indicated that soil labile organic carbons of the Pinus massoniana low-benefit forest of CR, CMS, RM were highly related.