稳定碳同位素揭示的滨海滩涂围垦土壤有机碳固定过程与机制

In this project, a typical soil chronosequence (unreclaimed wetlands and reclaimed lands with reclamation durations of 40, 70, and 100 years, respectively) cultivated with maize (C4 plant)/wheat (C3 plant) rotation was selected to reveal the incorporation process of new OC into soil aggregates based on stable carbon isotope (13C). The evolution of soil aggregates was firstly studied using soil physical fractionation method. The OC and 13C values of the whole soil, all aggregates, and POM fractions were further determined to understand their dynamics with reclamation durations. Based on the 13C values of reclaimed soil, unreclaimed tidal flat, and added straws (wheat and maize straws), the proportions of straw-derived OC (new OC) and tidal flat-derived OC (old OC) were quantified using a simple source mixing model. By comparing the location of new OC within each aggregate size class along the soil chronosequence, we will track the transformation process of the new OC among soil aggregates and OM fractions. The sequestration process and mechanism of new OC by reclaimed soils was then revealed based on the above evidences. This study will enhance our understandings of OC cycle in coastal reclaimed soils, and provided quantitative evaluations for OC sequestration in reclaimed soils.

为揭示滩涂围垦后急剧变化环境下的土壤有机碳循环特征和动态，本项目拟选择围垦历史阶段清晰、长期实行C4植物玉米和C3植物小麦轮作的典型滩涂区土壤为研究对象，以滩涂沉积物为参考，通过对不同年代围垦土壤进行团聚体和有机质组分分离实验，揭示长期旱作条件下土壤团聚体的演化趋势。在土壤物理分组的基础上，测定不同土壤团聚体和有机质组分的有机碳含量和13C值，利用稳定同位素质量平衡方程定量计算围垦后不同土壤团聚体和有机质组分中新老有机碳比例，通过对比分析不同年代土壤新加有机碳在团聚体和有机质组分中的分布特征，追踪新加有机质在土壤中的转化动态，揭示围垦土壤有机碳的固定过程。本项目的开展有助于深化对围垦土壤有机碳周转机制的认识，可为定量评估围垦土壤有机碳存储潜力提供科学依据。

土壤有机碳是影响气候变化和土壤肥力的关键要素，揭示不同土壤生态系统有机碳的固定过程与机制对于缓解全球气候变暖具有重要意义。大量研究通过模拟实验揭示了短期内土壤有机碳的动力学过程与机制，而有机碳在土壤中的周转速度较慢，长时间序列观测有机碳的动态过程更加贴合实际。本项目以滩涂围垦区为研究区，选择了围垦历史阶段清晰、长期实行C4植物玉米和C3植物小麦轮作的典型滩涂区土壤为研究对象，以滩涂沉积物为参考，通过对不同年代围垦土壤进行团聚体分离和相关指标分析测试，开展长期围垦条件下土壤有机碳组成及其潜在影响指标演变、快速变化环境下土壤有机碳动态的准确预测及其关键影响因素识别，土壤团聚体及其有机碳含量的演化及分布规律、土壤团聚体新老有机碳的占比及其动态。主要研究发现包括：（1）滩涂围垦后，土壤总有机碳、活性有机碳、惰性有机碳、氮、磷的养分元素及粉砂粒和粘粒含量呈逐年增长趋势，土壤pH、Ca、Na、Fe等指标呈逐步下降趋势；（2）经过对比，发现运用随机森林模型可准确预测土壤有机碳组分（总有机碳、活性有机碳、惰性有机碳）空间分布，土壤养分、盐分和pH被识别为影响土壤有机碳组分的关键因素；（3）随着围垦年限的增长，土壤<20 μm粒级团聚体含量整体呈增长趋势，而20-53 μm和53-250 μm粒级团聚体含量则随围垦年限的增长而略微下降；（4）随着围垦年限的增长，不同土壤团聚体新碳（围垦后新加入的有机碳）占比均呈现逐年增加趋势，且新加有机碳优先在大团聚体上富集，之后逐步转移至历经更小的团聚体。以上研究结果为深入认知长时间尺度土壤有机碳的周转过程提供了科学依据，对维持围垦区土壤生态功能、实现区域固碳减排具有重要意义。已发表学术论文4篇。