温带森林土壤有机碳矿化温度敏感性的海拔效应及控制机制研究

Understanding soil organic carbon stability is a global interest under the scenario of global change, but temperature sensitivity of soil organic carbon decomposition in temperate region, especially at altitude gradient is still uncertain because of the variability in the soil properties, environmental temperature and nutrient availability. Hence, we want to illustrate what controls temperature sensitivity of soil organic carbon decomposition: substrate availability, or soil characteristics and physical protection, or environmental regimes (temperature, N etc.), or site nature (vegetation). We hypothesize that soil organic carbon stability is likely a pseudo proposition without considering other factors while soil minerals protection plus nutrient (especially N) application would be the main factors influencing soil organic carbon decomposition. In order to prove this hypothesis, we use soil samples for incubations along altitudinal gradient in Changbai Mountain forest ecosystems in northeastern China. The respired CO2 was dynamically measured and the mineralization potentials of soil organic matter were evaluated at different temperatures. The incubated soil samples were collected periodically based on the dynamics of CO2 release. The variations in soil microbial community structure and the accumulation of microbial residues were measured at molecular level. The chemical structure of soil organic carbon was analyzed by using Infrared Spectroscopy and the functional components were identified with (Pyrolysis)-Gas Chromatography. The spatial distribution of organic carbon in soil particles were identified by particle size fractionation. Taken the physical, chemical and biological factors into account, the objectives of our research include: 1) to clarify the gradient effect on the temperature sensitivity of soil organic carbon decomposition; 2) to identify the thermodynamic and kinetics factors to control the decomposition potential of soil organic carbon, especially the C and N availability. The goal of this project is to deepen our understanding on key issues as related to soil organic carbon stability and sequestration in temperate forest ecosystem under the scenario of global warming.

在全球变化背景下，土壤有机碳矿化的温度敏感性是气候变化-碳循环反馈的决定因素。温带森林土壤具有高度的温度敏感性，但是有关不同海拔高度的温带森林土壤碳矿化的温度敏感性的影响因素和调控机制还不明确，碳氮耦合作用对有机碳库分解温度敏感性的影响也不得而知。因此，以长白山温带森林生态系统长期定位试验样地为依托，将原位土壤呼吸和土壤矿化培养实验结合，以土壤呼吸动态测定和温度敏感性评价为切入点，研究不同海拔高度土壤碳矿化动态对温度升高的响应。同时通过跟踪土壤碳矿化过程中微生物群落结构变化和残留物积累动态，分析土壤有机碳化学结构和不同热稳定性组分数量的变化，了解有机碳在不同粒级的空间分布及其保护作用，探讨碳氮耦合作用对土壤碳矿化的调控作用，阐明土壤碳矿化温度敏感性特征的海拔效应，明确影响土壤碳矿化机制的热力学和动力学因素以及主控因子，为系统评价温带森林土壤碳库对全球变化的响应与反馈提供理论基础。

温度作为影响土壤碳收支的重要因素，其对土壤碳库矿化及其温度敏感性的影响已受到广泛关注。由于海拔上天然的温度差，海拔梯度上土壤有机碳 (SOC) 循环转化特征已成为全球变化的研究热点。本研究选取长白山北坡不同海拔高度上的5个标准样地土壤为研究对象，通过测定土壤呼吸速率和长期培养后的土壤有机碳矿化速率，探讨了长白山森林土壤有机碳矿化温度敏感性的海拔效应及控制机制。.研究发现，在不同海拔梯度上，底物可利用性是土壤呼吸的控制因素，底物（基质）有效性增加可显著降低土壤呼吸的温度敏感性。在最低海拔处的阔叶红松林和最高海拔处的高山苔原土壤活性碳的相对比例显著高于其他植被群落下的土壤，因此具有更高的呼吸速率，但是温度敏感性降低，验证了“温度-质量”效应关系。长白山不同海拔高度土壤有机碳矿化潜力差异显著。虽然SOC矿化潜势在阔叶红松林土壤显著低于高山苔原土壤，但研究尚未发现海拔梯度上统一的变化规律，主要原因在于SOC矿化潜力受到了土壤质地和氮有效性的控制，掩盖了海拔梯度下气候条件对SOC稳定性的直接影响。不同海拔条件下SOC矿化符合三库动力学模型，并且SOC矿化特征主要取决于中等活性碳库的矿化。SOC的矿化受到碳库库容（热力学）和分解速率（动力学）的共同影响。土壤质地主要影响SOC的热力学特征即碳库的库容，而氮有效性主要影响SOC的动力学特征即可降解碳库的分解速率常数。不同海拔高度SOC长期矿化对温度的敏感性主要取决于土壤底物有效性，中海拔土壤有机碳分解对温度的敏感性显著高于低海拔和高海拔土壤。因此，温度升高对中高海拔土壤有机碳库分解的影响更为显著，对气候变暖形成正反馈作用。.通过明确不同长白山不同海拔高度上形成的SOC矿化特征以及温度敏感性并探讨其影响因素，对深入理解温带森林土壤有机碳的截获和稳定过程及其内在控制机理，尤其对于预测未来全球变化条件下碳循环的响应与反馈过程具有重要的指导意义。