农田土壤有机碳周转速率对土壤碳饱和度的响应机制及模型改进

The degree of soil organic carbon (SOC) saturation is a key factor determining SOC turnover in arable soils. Up to date, the SOC turnover rate was set as a constant value in the carbon cycling module in most of the models widely used, which led an increase in the discrepancies between measurements and simulations by enhancing external carbon input. It implies that the turnover rate of SOC was significant determined by the degree of SOC saturation, yet the responsive mechanisms and quantitative relationships between the degree of SOC saturation and SOC turnover rate remain unclear. Thus, three typical long-term cultivated soils (Luvic Phaeozems, Calcaric Cambisol and Eutric Cambisol, FAO) with different degrees of SOC saturation will be selected for an incubation trial with different levels of external carbon input (13C-labeled wheat straw) to clarify the mechanisms of SOC saturation impacts on turnover rate of external carbon (k1) and mineralization rate of SOC (k2) in soils, and further establish corresponding response functions for the relationships. In addition, the established response functions will be merged into a plant-soil model (SPACSYS) to replace the currently constant value of SOC turnover rate to modify the carbon cycling module, and parameterization and validation will be further achieved. The current project will enrich the knowledge of the mechanisms on the response of SOC turnover to soil carbon saturation, improve the precision of model simulations and the rationality of parameters, and provide theoretical basis for the optimization of agricultural managements to promote carbon sequestration in arable soils.

土壤碳饱和度是农田土壤有机碳周转的重要决定因素。当前多数模型在模拟农田土壤有机碳时将土壤有机碳周转速率假定为常数，导致模拟和观测值的差异随外源碳输入量增加而增大，这暗示土壤有机碳周转速率随土壤碳饱和度而变化，但其响应机制和定量关系尚不清楚。本项目以碳饱和度差异较大的黑土、潮土和红壤上3个典型农田长期试验为基础，通过室内培养，利用13C同位素标记的作物秸秆，设置不同碳输入水平，探明外源碳的固持效率和土壤原有有机碳的矿化速率对土壤碳饱和度的响应规律，建立其饱和动力学响应曲线，揭示土壤有机碳周转速率对碳饱和度的响应机制。同时，应用该响应曲线对作物-土壤模型（SAPCSYS）中土壤有机碳周转速率（常数）进行改进和验证，对比模型改进前后的模拟精度。研究结果将深化土壤碳饱和度对农田土壤有机碳周转影响机制的认识，提高农田土壤有机碳的模拟精度及参数合理性，为农田土壤固碳增汇技术集成优化提供科学依据。

土壤碳饱和度是农田土壤有机碳周转的重要决定因素。当前多数模型在模拟农田土壤有机碳时将土壤有机碳周转速率假定为常数，导致模拟和观测值的差异随外源碳输入量增加而增大，这暗示土壤有机碳周转速率随土壤碳饱和度而变化，但其响应机制和定量关系尚不清楚。本项目以碳饱和度差异较大的黑土、潮土和红壤上3个典型农田长期试验为基础，通过室内培养，利用13C同位素标记的作物秸秆，设置不同碳输入水平，探明外源碳的固持效率和土壤原有有机碳的矿化速率对土壤碳饱和度的响应规律，建立其饱和动力学响应曲线，揭示土壤有机碳周转速率对碳饱和度的响应机制。同时，应用该响应曲线对作物-土壤模型（SAPCSYS）中土壤有机碳周转速率（常数）进行改进和验证，对比模型改进前后的模拟精度。研究结果将深化土壤碳饱和度对农田土壤有机碳周转影响机制的认识，提高农田土壤有机碳的模拟精度及参数合理性，为农田土壤固碳增汇技术集成优化提供科学依据。