秦岭弃耕地自然恢复过程中土壤有机碳库变化及稳定机制

Agricultural abandonment has become one of major driving forces for global ecological restoration. However,our knowledge is deficient in the changes of stock, accumulation rate, and stability of soil organic carbon (SOC) during vegetation succession following agricultural abandonment. In the this research program, we will study the SOC dynamics(old carbon and new carbon) and stabilization mechanisms in ecosystems along a secondary succession gradient (i.e., grassland, shrub-grass land, young secondary forest, half-mature secondary forest, and mature secondary forest) following agricultural abandonment in China's Qinling Mountains. All the plots have been investigated in our previous stduy. Multiple techniques will be used in this study, such as organic matter fractionation, stable C isotopes (natural 13 C abundance of SOC, 13 C- and 15N-labelled litter incubation experiment),13C-NMR analysis, phospholipid fatty acids analysis, etc. The changes of accumulation rate, physical and chemical stability of SOC during vegetation restoration will be analyzed by measuring soil samples from different plot and different sampling years. The relationships among microbial community, SOC fractions and aggregate stability during vegetation succession will been explored. The 13 C- and 15N-labelled leaf and fine root will be incubated and decomposed in field in each stand to study the stabilization mechanisms of SOC derived from above- and belowground litter. Our study will reveal the SOC dynamics and stabilization mechanisms during vegetation restoration on abandoned croplands and enrich knowledge in soil C cycling.

耕地弃耕已成为全球生态恢复的主要驱动力，但是目前对于弃耕地恢复过程中土壤有机碳库及固碳速率的演变、土壤有机碳的稳定机制了解不足。本项目以秦岭不同自然恢复阶段弃耕地(草地、灌草地、幼龄次生林、中龄次生林及成熟次生林)为研究对象，在前期研究基础之上，通过定位观测，综合运用稳定同位素自然丰度法与人工标记法(用13C15N标记植物残体)、土壤有机碳分组技术、核磁共振分析、土壤微生物磷脂脂肪酸分析等方法，阐明弃耕地植被恢复过程中土壤"旧碳"与"新碳"的动态以及有机碳物理保护和化学稳定性的演变规律；明确不同恢复阶段弃耕地尤其是成熟林的土壤有机碳积累速率；探讨土壤有机碳组分-团聚体稳定性-微生物群落之间的关联性及其随弃耕地恢复的演变；揭示不同恢复阶段弃耕地地上和地下凋落物(叶和细根)新输入有机碳的稳定机制。本研究的结果将揭示弃耕地恢复过程中土壤有机碳库变化及稳定机制，丰富和发展土壤碳循环理论。

本项目以不同自然恢复阶段弃耕地为研究对象，通过定位观测及实验研究，综合运用稳定同位素自然丰度法与人工标记法、土壤有机碳分组技术、傅里叶红外光谱法、土壤微生物磷脂脂肪酸分析、土壤微生物高通量测序、土壤碳氮循环关键功能基因芯片分析等方法，研究了秦岭弃耕地自然恢复过程中土壤有机碳库变化及稳定机制。通过项目组成员四年研究，顺利完成了项目的各项任务，实现了项目的总体目标，完成了预期成果指标。主要取得了以下成果：（1）发现了森林恢复后，林龄、年均温、年均降水量驱动土壤有机碳动态的稳定同位素证据；研究结果推翻了国际同行（Giardina & Ryan）2000年曾发表于Nature的“土壤有机碳分解对温度不敏感”的经典证据。（2）揭示了秦岭弃耕地植被恢复过程中土壤有机碳库、有机碳组分及稳定性的演变规律及机制。（3）估算了秦岭弃耕地土壤有机碳积累速率、分解速率；建立了森林恢复过程中土壤“旧碳”与“新碳”动态变化的经验方程。（4）揭示了不同演替阶段弃耕地新输入有机碳在土壤中的动态变化规律及激发效应。（5）阐明了秦岭弃耕地植被恢复过程中，土壤有机碳的积累、土壤含水量及植被盖度的升高等变化导致土壤真菌和细菌群落呈现不同的演替模式。（6）揭示了弃耕地植被恢复驱动土壤有机碳分解速率升高、土壤微生物群落演替、土壤碳分解基因代谢潜能变化的机制。（7）项目已经发表标注基金号的SCI论文6篇。代表性论文发表于Global Change Biology、Plant and Soil等期刊。培养硕士研究生1名，合作培养博士研究生1名。

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