侵蚀坡面土壤碳排放效应及多因素耦合作用机理

Soil erosion seriously interferes with soil carbon dynamics and CO2 emission, and changes the ecosystem carbon cycle and carbon source-sink pattern. So far the effect of erosion induced CO2 emission is still a controversial scientific problem. At present, the research on the effect of erosion induced CO2 emission is mostly conducted based on the model estimation at the basin and regional scale, and the impact of the soil organic carbon level and time scale is rarely considered. To bridge the knowledge gap and meet the need for environmental impact assessment of soil erosion on the Loess Plateau, the project “Effects of erosion induced CO2 emission and the multi-factor coupling mechanism on slope scale” is proposed. Based on the erosion slope of different organic carbon levels in the hilly Loess Plateau, through long term erosion slope investigation, natural rainfall and simulated rainfall erosion observations, combining with13C isotope tracer and mineralization culture experiments, erosion induced changes of soil properties, soil environment conditions and soil organic carbon pool components will be tested, and the dynamics of erosion induced CO2 emission on different positon of the slopes will be continuously monitored using multi-channel and portable automated chamber system. The critical factors and multi-factors coupling effects on erosion induced CO2 emission will be revealed based on the structural equation modeling and mathematical Statistics. The short-term effect as well as long-term impact on erosion induced CO2 emission by on erosion and deposition areas will be clarified. The results will provide a scientific basis for the carbon emissions and carbon budget assessments in the erosion environment ecosystem.

侵蚀强烈影响土壤有机碳动态和碳排放，进而影响生态系统碳循环及碳源汇格局。侵蚀影响下土壤碳排放效应仍是存在较大争议的科学问题。目前有关侵蚀土壤碳排放效应的研究多以模型估算在流域和区域尺度展开，对土壤有机碳水平及时间尺度的影响关注不够。针对以上薄弱环节和黄土高原土壤侵蚀环境效应评估需求，项目以黄土高原丘陵区不同有机碳水平的侵蚀坡面为对象，以未侵蚀土壤为对照，通过长期侵蚀坡面观测和小区降雨试验，结合13C示踪和矿化培养实验，从侵蚀诱发坡面土壤理化生物属性、土壤水热环境、碳组分等的变化入手，采用多通道和便携式碳通量测量仪，观测侵蚀坡面土壤CO2排放动态；借助结构方程模型及数理统计方法辨析不同有机碳水平下侵蚀对土壤属性、土壤环境、碳组分及CO2排放的影响方式和程度，揭示侵蚀诱发土壤碳CO2放的多因素耦合作用机理，明确不同时间尺度下侵蚀坡面土壤CO2排放效应，为侵蚀影响下生态系统碳排放评估提供依据。

侵蚀强烈影响土壤有机碳动态和碳排放，进而影响生态系统碳循环及碳源汇格局。侵蚀影响下土壤碳排放效应是存在较大争议的科学问题。项目以黄土高原丘陵区不同有机碳水平的侵蚀坡面为对象，以未侵蚀土壤为对照，通过侵蚀坡面、侵蚀沟道、典型沉积区定位观测，结合13C示踪和矿化培养实验，从侵蚀诱发坡面土壤理化生物属性、土壤水热环境、碳组分等的变化入手，研究了不同有机碳水平下侵蚀坡面土壤呼吸的时空动态和时间尺度效应，探究了侵蚀和沉积效应对不同有机碳水平坡面土壤微生物群落的影响，解析了侵蚀作用下CO2通量的空间分异格局驱动因子及过程机制，分析了侵蚀坡面系统土壤碳排放效应及源汇关系转化条件。结果表明，土壤侵蚀加剧了坡面表层土壤理化生物属性、土壤水热的时空异质性，侵蚀降低了土壤细菌的α多样性，削弱了细菌网络的复杂性，侵蚀和沉积都导致真菌α多样性和网络复杂性降低，侵蚀坡面土壤CO2通量表现为沉积区>对照区>侵蚀区，这些时空异质性随有机碳水平升高呈非线性变化。在水热双因子模型的基础上，嵌入能够间接表征微生物活性和有效碳底物的C因子，分段区（按照坡面侵蚀部位）建立T&M&C模型，提高了侵蚀坡面CO2通量模拟精度。坡面土壤侵蚀-搬运-沉积过程中，11.40%-81.78%的土壤有机碳可被矿化，其中迁移至沉积区的有机碳中24.52%-82.66%可被矿化；侵蚀坡面原位CO2排放主要受其有机碳水平控制（-81%），异位排放主要受土壤含水量（37%）和温度（18%）的影响。侵蚀坡面不同部位碳排放的源汇效应存在差异，并在一定条件下发生转换。随着土壤有机碳水平提高，侵蚀坡面由碳汇逐渐转为碳源。当温度和土壤含水量分别超过约33℃和22%时，侵蚀区由碳汇转变为碳源。当土壤含水量超过8%时，沉积区主要是一个碳源。侵蚀坡面CO2排放的源效应约为2.35-2.47 t∙ha-2∙year-1，汇效应约为2.43-5.93 t∙ha-2∙year-1。该项目研究明确了侵蚀坡面土壤碳排放的多因素作用机制、碳排放源汇效应及其转换阈值，对制定面向固碳减排的侵蚀防控措施、评估侵蚀影响下生态系统碳排放有重要意义。