中亚热带山区土地利用变化 对土壤有机碳储量和质量的影响

通过对中亚热带山区天然林、人工林(用材林和经济林)、次生林、果园和坡耕地等7 种典型土地利用方式的土壤有机碳储量及质量的研究, 结果表明: 中亚热带山区天然林转变 为其他土地利用类型后, 土壤有机碳储量下降了25.6%~51.2%, 而表层0~20 cm 土壤有机碳 储量下降了45.1%~74.8%, 比底层土壤有机碳对土地利用变化的响应更为敏感。土壤轻组有机碳储量(0~60 cm) 下降了52.2%~84.2%, 轻组有机碳占总有机碳比例从13.3%降到3.0% ~10.7%, 比土壤总有机碳对土地利用变化更为敏感。天然林转变为其他土地利用类型后土壤 有机碳损失巨大的原因主要与凋落物归还数量及质量, 水土流失和经营措施对土壤(特别是表层土壤) 的扰动引起土壤有机质加速分解等因素有关。坡耕地人为干扰最严重, 土壤有机 碳下降幅度最大。中亚热带山区土地利用变化引起土壤有机碳储量下降幅度高于全球平均水平, 主要与区域降水和地貌条件有关。因此, 保护山区脆弱生态环境, 加强天然林保护和植 被恢复, 合理营造人工林, 减少耕作, 对山区土壤碳吸存、减缓大气CO₂ 浓度升高和气候变化以及促进山区可持续开发的生态服务功能发展都具有重要意义。

The Impact of Land Use/Cover Change on Soil Organic Carbon Stocks and Quality in Mid- subtropical Mountainous Ar ea of Southern China

Land use/cover change (LUCC) is widely recognized as one of the most important driving forces of global carbon cycles. The influence of LUCC from native forest to plantations, secondary forest, orchard and arable land on soil organic carbon (SOC) stores and quality was investigated by using "space for time" method in mid-subtropical mountainous area of southern China. The results show that LUCC has led to great decreased SOC stocks and quality. Considerable SOC and light-fraction organic carbon (LFOC) have been stored in native forest (142.2 t hm^-2 and 14.8 t·hm^-2, respectively). When native forest was converted to plantations, secondary forest, orchard and arable land, the SOC stocks decreased by 25.6% -28%.7%, 38.0%, 31.8% and 51.2%, respectively. The LFOC stocks decreased by 52.2-57.2% when native forest was converted to woodland plantations and second forest, and by 82.1% -84.2% when to economic plantation, orchard and arable land. After the conversion, the ratios of LFOC to SOC (0-60 cm) decreased from 13.3% to about 3.0%-10.7%. The SOC and LFOC stored in the upper 20 cm soil were more sensitive to LUCC when compared to the subsurface soil layer. Comparison suggests that the effects of the above mentioned LUCC on carbon release and quality deline were greater than the global average level, which could be explained by the vulnerable natural environment and special human management practices. Thus, it is significant to protect vulnerable environment, restore vegetation coverage and afforest plantation reasonably in mountainous area in mid-subtropics, for enhancing soil carbon sequestration, mitigating elevated atmospheric CO₂ and sustainably developing ecological services.