区域环境要素对栓皮栎次生林生态系统土壤有机质稳定性的影响机制

On a global average, almost two-third of all forest is secondary forest or other naturally regenerated forest except primary forest, which represents a huge reservoir of carbon on a global basis. Yet, despite their importance in the global carbon budget and their high susceptibility to climate change, very litter is known about how environmental change will affect the stabilization of soil organic matter (SOM) in secondary forest. It remains largely unknown why some SOM persists for millennia whereas other SOM decomposes readily and this limits our ability to predict how soils will respond to global environmental change..Six typical Quercus variabilis natural secondary forests has been selected to establish a gradient of environment, and double-labeled with 15N technique were used to simulate nitrogen deposition. By investigating the SOM and relevant environments, the influences of environment on litter quality and quantity, soil carbon cycling, soil microbial diversity and activity, nutrient composition (elemental and isotopic), as well as physic-chemical properties of soil. In an effort to elucidate why organic matter in subsoil horizons has longer turnover times than topsoil as an ecosystem property. To systematically explore the influence of environmental change on soil carbon stability of the natural secondary forest ecosystems across Eastern China and the underlying mechanisms. .Under the context of global change, in order to understand the impact mechanism of regional environmental change on the stabilization of SOM better, we select the single species dominated secondary forest ecosystems on the cross-regional scale as the research object to simplify the influence of the different dominant tree species on the quality of soil organic matter through. .It offers great potential for revealing the mechanisms underpinning soil carbon stability and has great implications for global environmental change prediction and forest management formulation.

次生林占全球森林覆盖面积的57%，作为全球巨大的碳库之一，它对气候变化具有高度的敏感性，在全球碳平衡中起着极其重要的作用，然而，未来环境变化对次生林生态系统土壤有机质稳定性的影响却了解甚少。本项目选择区域尺度上6个典型栓皮栎次生林样点，通过建立自然环境变化梯度及模拟氮沉降的稳定性核素15N双标记试验，研究环境的改变对森林凋落物的数量和质量、有机质的组成和分解、微生物多样性及其活性等的影响；从生态系统的角度探讨深层的土壤有机质比浅层稳定的原因，揭示区域环境变化对我国东部次生林生态系统土壤有机质稳定性影响的潜在机制。在全球变化的背景下，选择跨区域尺度上单一树种为主的次生林生态系统为研究对象，简化了优势树种的不同对土壤有机质质量的影响，能够更好的揭示环境对土壤碳稳定性的影响机制；在分析和预测全球环境变化效应，预测土壤对环境的敏感程度，制定我国合理森林经营管理政策等方面均具有重要的理论和实践意义。

次生林占全球森林覆盖面积的57%，作为全球巨大的碳库之一，它对气候变化具有高度的敏感性，在全球碳平衡中起着极其重要的作用，然而，未来环境的变化对次生林生态系统土壤有机质稳定性的影响却了解甚少。本项目综合核磁共振、元素和稳定同位素的技术方法来探讨环境要素对区域尺度上栓皮栎次生林生态系统土壤有机质稳定性的影响；同时利用稳定同位素标记的方法，探讨自然环境梯度（不同温度和降水条件下）和模拟氮沉降对栓皮栎不同类型凋落物分解过程以及土壤有机质形成与稳定的影响。研究结果表明，在区域尺度上，亚热带南部的两个点土壤表层由于缺乏Oa层，土壤有机质明显少于其北部的样点。而在纬度梯度上，0-10cm层土壤有机碳储量并没有明显的分布规律，而是与土壤质地有关；亚热带区的栓皮栎次生林土壤有机质的分解程度比暖温带更高；土壤pH是控制土壤有机质分解程度的最主要因素；随着土壤深度的增加，δ13C和δ15N升高，而C/N比降低，表明其分解程度也更高；提出在区域尺度上A/M比是评价土壤有机质稳定性的一个很好的指示指标。通过分析区域尺度上栓皮栎次生林生态系统表层土壤微生物群落结构发现，温度和降水量是影响该区域土壤微生物群落组成最主要的因素，真菌和细菌的丰度与温度和降水量有显著负相关；土壤的理化性质（pH、N的有效性、土壤C/N比等）对土壤微生物群落结构影响居其次。通过为期一年的15N标记栓皮栎凋落物分解的研究，发现自然环境梯度（温度和降水梯度）和N素添加对不同类型凋落物早期分解过程的影响差异并不明显。该研究结果对分析和预测全球环境变化效应，预测土壤对环境的敏感程度，制定我国合理森林经营管理政策等方面均具有重要的理论和实践意义。