中文摘要：

对中亚热带山区天然常绿阔叶林、次生常绿阔叶林、人工林（针叶林和阔叶林）、柑橘园和坡耕地等典型土地利用方式土壤CO2排放连续3a定位观测,结果表明：天然林改为其它土地利用方式后,土壤CO2排放量显著减少32%～63%,主要原因为地上凋落物归还量减少,地下细根生物量和周转下降,频繁人为干扰和严重水土流失引起土壤有机碳库数量和质量大幅下降。本区天然林改为次生（人工）林,土壤CO2排放量减幅（32%～48%）高出热带平均水平（29%）,改为农业用地,土壤CO2排放量减幅（50%～63%）高出全球平均水平（33%）。

英文摘要：

Using ＂space for time＂ method, the influence of land use/cover change （LUCC） from natural forest to secondary forest, plantations, orchard and sloping tillage on soil CO2 efflux was evaluated in mid-subtropical mountainous area in South China. Results showed that the soil CO2 effiux rate was significantly reduced by 32% -63% after the land use changes. Concomitantly, soil carbon input from the litter-fall, fine root turnover, and soil organic carbon storage and quality were remarkably declined. The highly intensified human disturbance （slash and burning, cultivation, weed and fertilization） led to serious soil and water losses and rapid decomposition of soil organic matter. After the natural forest was converted to secondary forest and plantations, the soil CO2 efflux rate was reduced by 32% -48% , which was higher than the average level in tropics （29%）. Whereas the reduction of soil CO2 efflux rate （by 50% -63% ） after the transformation from natural forest to agriculture land was higher than the global average level. Owing to the potential vulnerable natural environment （frequent heavy rain and steep slope）, the reduction levels of fine root turn over rate and soil organic carbon storage induced by the land use change in mid-subtropical China were much higher than the tropical or the global average level. This might be the major reason of the higher reduction level of soil CO2 efflux rate in this geographical region than the tropical or the global average level following the land use changes.