古水稻土残存有机碳的特征及其稳定机理

Enhancing soil organic carbon (C) stock is one of the important approaches to slowdown the rise of atmospheric CO2 concentration. Most of the studies have focused on organic C sequestration in topsoils, while the understanding of organic C in subsoils with huge potentiality of C sequestration is very limited. The buried ancient paddy soils distributed abundantly in the Yangtze River Delta are the ideal materials for the research into the subsoil organic C. Using advanced solid-state nuclear magnetic resonance (NMR) techniques in combination with chemical analyses, we will examine the density & size-particle distribution of C contents and chemical compositions of organic C samples prepared from ancient paddy soils differing in burial duration and environmental conditions, and identify the main stable organic C components. Then we will examine the sources (of plant or microbial origin) and molecular forms of these stable components through compound-specific tests and selective spectral editing NMR techniques. At last, based on the relationships between chemical structure, residence and stability performance, in combination with the relevance of burial environmental conditions, we will elucidate the stabilization mechanisms of the surviving organic C in ancient paddy soils. In addition, by comparing the differences in characteristics of organic C between modern paddy topsoils and adjacent ancient paddy soils, we will predict the evolution trend of the organic C stock newly formed by burying the former due to land development. This study will advance the understanding of long-term stability of organic C stock in subsoils, and may provide a new theoretical and technical support for enhancing soil organic C sequestration.

增加土壤有机碳库是减缓大气CO2升高的重要途径之一，目前大部分研究关注于土壤表层有机碳固定的研究，而对具有巨大固碳潜力的土壤下层有机碳的认识十分有限。长江三角洲广泛分布的埋藏古水稻土是研究下层土壤有机碳的绝佳材料。本项目将采用高级固态核磁共振(NMR)技术并结合化学分析，研究长三角地区不同古水稻土残存有机碳的含量、化学组成及其粒级赋存分布，识别出主要的稳定有机碳组分，并进一步通过专一性化学检测或选择性NMR图谱编辑技术分析其来源（植物性或微生物性）及其分子形态。最后，根据化学结构、赋存分布与稳定性的关系，并结合对埋藏环境条件的分析，解析古水稻土残存有机碳的长期稳定机理。另外，本研究也将通过比较现代水稻土有机碳与古水稻土残存有机碳的性质差异，预测现代水稻土掩埋所形成的有机碳库的变化趋向。本研究将推进对下层土壤有机碳库长期稳定性的认识，并可能为土壤有机碳库扩增提供新的理论依据和技术途径。