广西喀斯特移民迁入区土地利用变化对土壤有机碳和全氮储量的影响

土地利用变化是影响土壤碳、氮循环的重要因素,也是研究全球气候变化的热点.本研究基于固定深度法(FD)和等效质量法(ESM),从森林开垦和退耕还林还草两个角度探讨喀斯特移民迁入区土地利用变化对土壤有机碳(SOC)和全氮(TN)储量的影响.结果表明: 原始森林被开垦为草地、桉树林和农田后,SOC和TN储量均显著减少;基于FD方法计算的SOC和TN储量分别损失了47.4%、41.6%,而通过ESM方法计算的SOC和TN的损失率分别为54.8%、49.7%.农田撂荒为草地及种植桉树后,SOC和TN储量显著增加;基于FD方法计算的SOC和TN储量提高了60.5%、49.7%,通过ESM方法计算的SOC和TN分别增加85.5%和70.8%.FD方法忽略了土地利用变化后土壤容重的差异,而森林开垦后会显著增加土壤容重,因此,FD方法高估了SOC和TN储量;农田恢复后土壤容重减小,FD方法则会低估SOC和TN储量的增加.建议相关研究选择ESM方法测算土地利用变化对SOC和TN储量的影响.

Effects of land use change on soil organic carbon and total nitrogen storage in Karst immigration regions of Guangxi Province,China.

Land use change is an important factor affecting soil carbon and nitrogen cycle, and this is a hot spot in the study of global climate change. Based on the fixed depth method (FD) and the equivalent mass method (ESM), we explored the effects of land use change on soil organic carbon (SOC) and total nitrogen (TN) storage from the perspectives of forest reclamation and farmland vegetation restoration in Karst area. The storage of SOC and TN significantly decreased after the fore-sts were converted to grassland, eucalyptus and farmland. On average, the SOC and TN losses calculated by the FD method were 47.4% and 41.6%, respectively, the losses of SOC and TN calculated by ESM method were 54.8% and 49.7%. The SOC and TN storage increased significantly after abandonment of farmland to grassland or planting eucalyptus. On average, the SOC and TN stocks calculated based on the FD method increased by 60.5% and 49.7%, while the SOC and TN calculated by the ESM method increased by 85.5% and 70.8% respectively. The difference between FD method and ESM method was analyzed, it was concluded that FD method ignored the difference of soil bulk density after land use change. Soil bulk density was significantly increased after forest destruction. The loss of SOC and TN storage was overestimated by the FD method. Soil bulk density decreased after vegetation restoration, FD method will underestimate the enhancement of SOC and TN storage. It is suggested that the ESM method should be used to estimate the impacts of land use change on SOC and TN storage.