亚热带森林生态系统深层土壤有机碳的动态及维持机制

Despite their low organic carbon concentration, subsoil horizons in forest ecosystems contribute more than half of the total soil carbon stock. Therefore, their dynamics may have significant effects on regional and global carbon cycle. Since soil carbon is far from saturated in deep soils, it has an enormous potential to act as a carbon sink. In general, deep soil horizons contain large quantities of recalcitrant carbon characterized by high residence time. Stabilization of the deep soil recalcitrant carbon is controlled by several different mechanisms, including stable chemical composition and structure, protection from soil aggregates, and association with soil minerals. These mechanisms vary among geographic locations, land cover and soil genesis processes. However, these stabilization mechanisms can be reversed, especially under novel environmental conditions caused by global change. Thus, in the context of global change, human activities can significantly affect the dynamics of recalcitrant carbon in deep soils by directly or indirectly altering the soil environment. Until recently, few studies have been conducted to examine the how changes in environmental factors may affect deep soil carbon dynamics. Even for the few studies, their conclusions are inconsistent and sometimes controversial. So this poses a huge research need to better understand stabilization mechanisms and dynamics of subsoil organic carbon and how it may be affected by different environmental factors...In this study, we are going to sample soils from different horizons in a forest ecosystem in subtropical mountain areas in China. Surface and deep soil samples will be analyzed to characterize their physical and chemical properties. Field experiments will be designed to examine how surface and deep soils respond differently to added nitrogen input, and change in precipitaton pattern. Soil samples will be incubated in the lab to examine their responses to environmental changes like elevated CO2, increased temperature, modified precipitation pattern, and increased nutrient level. Through this study, we'll gain a better understanding of the dynamics and stabilization mechanisms of deep soil carbon and how it may react to future global change, thus to reduce the uncertainties in predicting how deep soil organic carbon pool may respond to global change.

尽管深层土壤中有机碳的浓度比较低，但其总量占土壤碳含量的大约一半左右， 所以它的微小波动都会对全球碳循环产生重要的影响。全球变化导致了许多环境条件的改变，有可能会对深层土壤有机碳的稳定机制产生重大影响，从而影响碳循环。现有的为数不多的关于深层土壤有机碳动态及其影响因子的研究得到的结论是不一致的，有时候甚至是互相矛盾的，这更凸显了综合研究深层土壤有机碳动态及其稳定机制的必要性。本研究将以亚热带山地森林土壤为例，利用野外采样、野外实验及实验室培养等方法，通过对表层和深层土壤样品进行分析，比较它们理化性质的不同；通过野外实验，研究土壤对添加无机氮，降水增加的反应，测定土壤呼吸的变化；通过实验室土壤培养，监测其对温度升高、CO2浓度增加、水分条件变化、及添加营养物等处理的响应。本研究的结果将有助于加强我们对深层土壤动态及稳定机制的理解，增强预测深层土壤对全球变化响应的能力。

深层土壤中有机碳的浓度较低，但其总量占土壤碳含量的大约一半左右，所以它的微小波动都会对全球碳循环产生重要的影响。全球变化导致环境条件的改变，为此，有必要了解影响深层土壤碳矿化的主要因素，并掌握活性碳源、氮源输入对深层土壤碳矿化和固持的影响，以利于在未 来气候变化条件下对深层土壤有机碳的预测和管理。.本项目以亚热带山地森林土壤为例，对表层和深层土壤样品进行分析，比较它们理化性质的不同；通过野外实验添加无机氮，凋落物处理，降水处理的反应，测定土壤呼吸的变化；通过室内土壤培养，分析深层土壤碳矿化特征及其影响因素。.结果表明亚热带山地森林土壤具有很高的空间异质性，表层土壤（0-10 cm）碳氮的空间变异程度高于亚表层土壤（10-30 cm）。环境与空间因子对表层土壤有机碳空间变异的解释力（47.8%）高于亚表层土壤有机碳（24.4%）。利用高光谱技术可以成功对表层和亚表层土壤有机碳（SOC）和全氮（TN）的进行反演预测（R2为0.66-0.9）。利用spiking法并借助加权算法，使得光谱预测模型在不同土壤层次间的传递性得到大幅提升。凋落物加倍和去除对土壤呼吸有显著影响，而持续了1年的氮添加对森林土壤呼吸没有明显影响。.深层土壤有机碳的矿化能力显著低于表层土壤，主要受到活性碳源和氮源的限制。活性碳源添加后可刺激所有土壤原有有机碳的矿化（激发作用），但深层土壤的激发作用强度显著高于表层土壤。表层土壤和深层土壤不同的碳矿化格局及其对活性碳源输入的不同反应主要受微生物群落底物利用格局的影响。表层土壤中碳氮的矿化呈现出显著的相关关系，而这一关系在深层土壤中并不存在。.本研究对亚热带森林土壤的空间变异及其主要影响因素的研究结果有助于理解土壤碳氮空间格局形成的相关生态过程，阐明了底物有效性和土壤微生物的底物利用格局在调节土壤碳氮矿化中的重要作用，为预测深层土壤对全球变化响应提供理论依据和数据支持。

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