地膜覆盖对旱作玉米农田土壤有机碳转化和稳定性的影响及其机制

Plastic film mulching is an effective measure to improve the dryland productivity in the Loess Plateau and has become one of the most widely used agricultural cultivation technique in this area. As for the academic world, however, the center of attention on the film mulching has shifted from the initial crop yield enhancement to its ecological sustainable development. Among these concerns, the response of capacity and stability of soil organic carbon (SOC) to long-term film mulching has become a top priority issue, due mainly to the fact that SOC is the foundation of soil fertility. Unfortunately, there is a serious lack of understanding on effects of long-term film mulching on transformation and stability of soil organic carbon and their driving mechanism. Using both soil aggregate classification and stable isotope tracer methods, this proposed project will incorporate a long-term film mulching experiment into the verification test to explore: the response of soil aggregate composition structure and stability to long-term film mulching; the different effects of short- and long-term film mulching on the soil aggregate SOC contents; the different allocation proportion of rhizodeposition-related carbon and stubble decomposition-derived carbon to soil aggregate SOC pools and their respective contribution to the stability of soil carbon pool. In this light, the project will further investigate the manner and mechanism of plastic film mulching affecting SOC transformation and stability of soil organic pool. The results can be expected to provide the theoretical basis for the evaluation of sustainability of film mulching cultivation and the design of regulating strategy for stabling soil carbon pool.

地膜覆盖是提升黄土高原旱作农田生产力的有效举措，已成为该区应用面积最广的农业栽培技术。但学术界对覆膜措施的关注已从最初的产量提升，开始转向其生态的可持续性发展。其中，土壤有机碳作为土壤肥力的基础，其库容和稳定性对地膜覆盖的响应已成为关注的首要问题。然而，目前就长期覆膜对土壤有机碳库及其稳定性作用机理的认识仍非常缺乏。本项目拟将长期覆膜玉米定位试验与机理验证试验相结合，把有机碳的内部分解与外部补充两个逆向过程相联系，并利用团聚体分级和同位素示踪技术重点解决：不同覆膜年限对土壤团聚体组成结构及稳定性的影响；不同稳定性的团聚体有机碳转化与稳定对长/短期覆膜处理的差异响应特征及规律；玉米根际沉积碳和根茬分解碳在不同团聚体有机碳中的分配及其对碳库稳定的相对贡献等科学问题。据此，探索地膜覆盖影响旱作农田土壤有机碳转化与稳定的途径及机制，为覆膜技术可持续性的评价及土壤碳库稳定的调控策略制定奠定理论基础。

在黄土高原半干旱雨养区，地膜覆盖技术的集成创新和广泛应用为旱作农田生产力的提高和区域粮食安全做出了巨大贡献。然而，长期覆膜措施的生态可持续问题也逐渐凸显。其中，作为农田肥力基础的土壤有机碳，其库容和稳定性对覆膜管理的响应是学界关注的首要问题。对该科学问题的解答，需要揭示长期覆膜条件下土壤有机碳库及其稳定性的演变特征，及其背后驱动有机碳转化的关键途径。据此，本项目依托长期覆膜玉米定位试验和区域覆膜农田多年多点整合数据，并利用团聚体分级和同位素示踪技术探讨了不同覆膜年限对土壤有机碳组分和土壤团聚体组成的影响；玉米根际沉积碳和残茬分解碳在不同团聚体中的分配及其对碳库稳定的相对贡献；同时从区域尺度上探究了覆膜措施对旱作农田土壤碳、氮循环关键生态过程的影响。研究发现：随覆膜年限延长，土壤有机碳能够在覆膜前期积累，而在后期下降；覆膜处理增加土壤有机碳具有最佳的覆膜年限限制。旱作玉米农田随着覆膜年限的延长，惰性碳库首先出现快速的下降，随后逐渐回升，最终可恢复甚至超出初始水平。地膜覆盖能够显著改善土壤团聚化程度。覆膜措施促进植物更多地固定大气二氧化碳转化成光合产物，这种地上光合生产能力的提升与地下碳的分配幅度是正相关的。地膜覆盖通过更强烈的根际沉积作用向土壤中输入更多的光合碳。并且，由于地膜的阻隔，更多的光合碳能够较长时间地储存在土壤中，覆膜导致较少的光合碳释放到大气中。覆膜条件下，作物残茬来源碳在土壤小团聚体和化学稳定性高的碳组分中的分配比例更多。区域尺度上，覆膜措施能够维持，甚至增加旱作农田土壤碳库，主要归结于更多的作物来源的碳投入。上述研究结果可为旱作区覆膜农田土壤碳库的调控对策设计、旱区覆膜农业生产力的可持续提升奠定科学基础。