基于三库一级模型的红壤区土壤碳库稳定性估算及其对秸秆还田的响应机制研究

Currently，global warming has been an indisputable fact, and what the key matter is how to take effective measures to reduce greenhouse gas emissions in response to climate change. The variation in the stability of cropland soil organic carbon pool will significantly affect the Changes in atmospheric carbon dioxide concentrations. Yet it is still controversial of the effect of carbon sequestration via straw return, which is the most popular carbon sequestration measure. Thus, how to quantify the stability of soil organic carbon pool with highly complex constituents, and then effectively controlling its stability, will importantly and positively contribute to soil carbon sequestration and global climate change. To solve these problems above, this project plan to select Dongxiang County, Jiangxi Province as the study area, based on the applicant’s historical soil survey data, we will conduct a new round of soil survey, especially the survey of straw return, and collect soil samples accordingly. The samples will be analyzed based on a combination method of acid hydrolysis and CO2-C release during a 100-day incubation. The data from acid hydrolysis-incubation experiments were fitted to a three-pool first-order kinetics model that divided SOC into active, slow and resistant carbon pools. Meanwhile, with the same analytical method, we can obtain the mean residence times of the active and slow carbon pools in soils and evaluate their stability levels in this way. Then, the corresponding soil physicochemical properties will be analyzed and the variation in cropland soil carbon fluxes with different straw return scenarios will be determined in the fields, all which will reveal how straw return takes effect on the soil properties and soil incubation to impact on the stability of the different soil organic carbon pools over the latest decade. Finally, we hope that a long-acting strategy on increasing soil carbon pool through straw return will be put forwarded in the red soil region.

当前，全球气候变暖已是不争事实，如何采取有效措施以减少温室气体排放是应对气候变化的关键所在。农田土壤有机碳库稳定性的改变将会对大气CO2浓度的变化产生显著影响，同时秸秆还田作为当前最为普遍的固碳措施其固碳效果尚有争议。因此，如何量化构成复杂的土壤有机碳库的稳定性，进而通过秸秆还田来有效调控土壤有机碳库的稳定性，对土壤固碳和全球气候变化具有重要积极意义。本项目拟选择江西省东乡县作为研究区，基于历史土壤调查数据，开展新一轮农田秸秆还田调查，采集土壤样品，于室内进行土壤呼吸培养实验和酸水解实验，借助三库一级动力学模型获取土壤活性、慢性和惰性碳库大小及其平均驻留时间，重点估算土壤有机碳活性和慢性碳库的稳定性水平，同时分析相应地土壤理化性质以及检测野外农田土壤碳通量变化，揭示近10年秸秆还田如何通过改变土壤性质和土壤呼吸，进而影响土壤有机碳各分库的稳定性。最终，提出红壤区秸秆还田长效提升土壤碳库策略

如何有效量化土壤有机碳库稳定性并厘清其对秸秆还田的响应是农田土壤长效固碳亟需解决的重要科学问题。本项目选取了红壤典型区－江西东乡作为研究区，基于历史数据，开展新一轮农田调查，结合土壤呼吸培养实验和三库一级动力学模型，获取土壤活性（Ca）、缓效性（Cs）和惰性碳库（Cr）数据，利用土壤有机碳组分构成和平均驻留时间来刻画研究区土壤有机碳库稳定性时空变化，并通过统计分析揭示近10年土壤有机碳组分库对土壤属性和秸秆还田比例的响应。主要结果为：（1）2009-2019江西东乡地区表层水稻土平均总有机碳（TOC）、Ca和Cs呈现减少，而Cr均值增加；TOC、Ca、Cs和Cr变化速率分别为-0.04 g·kg-1·year-1、-0.02 g·kg-1·year-1、-0.07 g·kg-1·year-1和+0.05 g·kg-1·year-1（P > 0.05）。土壤属性对2019年东乡地区表层水稻土TOC、Ca和Cr的空间变异影响较小，其中，土壤TN同时对TOC、Cs和Cr变异贡献较大;（2）东乡2019年红壤性水稻土表层土壤活性碳库平均驻留时间（MRTa）与缓效性碳库平均驻留时间（MRTs）均值分别为26.5 d和14.1 a，与2009年相比，未发生显著性变化。整体上，东乡南部地区活性碳库和缓效性碳库更为稳定，且东乡地区红壤性水稻土MRTa与MRTs存在明显的时空分异，不同地理位置的MRTa与MRTs变化幅度分别达-1.3%~544.5%和-6.7%~1375.5%。这种时空变异，部分源于土壤活性碳和缓效性碳组分构成的空间分异；（3）与其它研究区相比，江西东乡活性碳库较小，但其在土壤驻留时间更长；由于不同点位秸秆还田比例存在差异，该地区表层土壤有机碳组分库空间分异明显，其中Cs和Cr空间变异受秸秆还田比例影响较大，且Cs变异受之影响更甚；长期秸秆还田下，TOC和Cr空间分异更容易受到碱解氮的限制。因此，南方红壤区稻田土壤有机碳库对长期秸秆还田响应更为敏感的是Cs，而不是Ca；在制定水稻土固碳措施时，应关注土壤N含量尤其是碱解氮的协同变异。