长期植稻土壤团聚体有机碳组分的演变规律及其潜在固持机制

Evolution Patterns and Underlying Sequestration Mechanisms of Organic Carbon Components in Soil Aggregates under Long-term Rice Cultivation

摘要:

水稻土是长期水耕熟化形成的一种人为土壤，具有较高的有机碳储量和固碳潜力。阐明稻田土壤有机碳的保护机制，可为稻田土壤的固碳减排和可持续利用提供理论依据。借助我国东部沿海滩涂围垦后形成的1 000年水稻土时间序列，结合力稳性团聚体分级和物理颗粒/密度分组等手段，研究长期植稻下土壤团聚体内闭蓄态/游离态和颗粒态/矿物结合态有机碳的分布特征及演变规律。结果表明：长期植稻下土壤有机碳逐渐积累的同时，颗粒态有机碳（POC）和矿物结合态有机碳（MOC）含量也随之提高，但以MOC为主，占总碳库的64.40%~87.89%。不同植稻年限土壤中各粒径团聚体的分布规律一致，依次为大团聚体（74.0%~77.6%）、微团聚体（9.2%~15.9%）和黏粉粒级微团聚体（8.6%~15.7%），进而超过70.00%的碳储存于大团聚体中。各粒径团聚体有机碳含量均随植稻年限和粒径大小的增加而增加，具体表现为7.39~13.78 g·kg-1、1.72~2.74 g·kg-1和0.66~1.92 g·kg-1。不同形态团聚体中主要以MOC为主，在大团聚体、闭蓄态和游离态微团聚体中MOC 最高可达POC的2.9倍、1.1倍和3.2倍。闭蓄态微团聚体对POC的保护作用强于游离态微团聚体，具体表现为闭蓄态微团聚体中POC含量最高可达游离态的1.5倍。在团聚体的物理保护下，长期植稻有利于有机碳的固定，而闭蓄态微团聚体对颗粒态有机碳的保护作用是稻田土壤有机碳固持的潜在机制。

Abstract:

【Objective】Paddy soil is a type of anthropogenic soil formed through long-term water cultivation and ripening, which has a high organic carbon storage and carbon sequestration potential. Clarifying the protection mechanisms of organic carbon in paddy soil can provide a theoretical basis for carbon sequestration, emission reduction, and sustainable utilization of paddy soil. 【Method】Using a 1000-year chronosequence of paddy soils formed through coastal reclamation in Eastern China, we investigated the distribution characteristics and evolution patterns of occluded/free and particulate/mineral-bound organic carbon within soil aggregates under long-term rice cultivation. This was achieved through methods such as force-stable aggregate fractionation and physical particle/density grouping. 【Result】While soil organic carbon (SOC) gradually accumulated under long-term rice cultivation, the contents of particulate organic carbon (POC) and mineral-bound organic carbon (MOC) also increased. However, MOC was the dominant form, accounting for 64.40%~87.89% of the total SOC pool. The distribution patterns of different size soil aggregates were consistent, with macroaggregates (74.0%~77.6%) being the most abundant, followed by microaggregates (9.2%~15.9%) and silt and clay-sized microaggregates (8.6%~15.7%). Therefore, over 70.00% of SOC was stored in the macroaggregates. The organic carbon content of aggregates of all particle sizes increased with the increase of paddy cultivation age and grain size, which were 7.39~13.78 g·kg-1, 1.72~2.74 g·kg-1 and 0.66~1.92 g·kg-1. Among different types of soil aggregates, mineral-bound organic carbon (MOC) was the dominant form. In macroaggregates, occluded microaggregates, and free microaggregates, the MOC contents were up to 2.9, 1.1, and 3.2 times higher than POC, respectively. The protective effect of occluded microaggregates on POC was stronger than free microaggregates, with the POC content in occluded microaggregates being up to 1.5 times higher than in free microaggregates. 【Conclusion】Long-term rice cultivation is beneficial for SOC sequestration under the physical protection of soil aggregates. The protective effect of occluded microaggregates on POC is a potential mechanism for carbon sequestration in paddy soil.