土壤团聚体有机质周转过程中碳、氮动态研究

Aggregate turnover is a key process of soil development, which promotes soil organic matter stabilization by hindering decomposition of particulate organic matter and its interactions with mineral particles. Soil organic matter stabilization processes lead to 13C and 15N fractionation and consequently to various δ13C and δ15N values of soil organic matter fractions. Differences in δ13C and δ15N within the aggregates and fractions may has reason which stabilization of organic materials after passing one or more microbial utilization cycles, leading to heavier 13C and 15N in remaining soil organic matter. We hypothesized that: C and N isotopes fractionation occur in turnover of soil aggregates, and 13C and 15N exhibit enrichment from macro- to micro-aggregates. In this study, the aggregate-associated organic C and N pools and soil δ13C and δ15N are studied, and the soil aggregate respiration characteristics as well as organic N mineralization process were also compared. The purpose of this study was to determine how fractionation of C and N isotope was affected by aggregates turnover, to analyze the distribution of different age organic matter in soil aggregate, to quantify the contribution of aggregates to soil C emission and N supplying capacity, and to propose an extended scheme of C and N flows between the aggregate size classes and soil organic matter fractions. This study suggested and demonstrated the validity of a new approach for tracing carbon and nitrogen dynamics in turnover of soil aggregate associated organic matter based on stable isotopic techniques. The results could enrich the theory of soil aggregates.

土壤团聚体周转过程是土壤发育的关键过程，其通过抑制颗粒有机物的分解和矿物颗粒的相互作用促进有机质固定。有机质固定导致碳氮稳定同位素分馏，使不同组分中δ13C和δ15N值多样化。其可能原因是，土壤微生物对有机质分解利用过程中, 轻同位素优先分解，残留在土壤中的重同位素比例增加。据此假设：土壤团聚体有机质周转会造成碳氮同位素分馏，且13C、15N同位素随着时间从大团聚体向微团聚体富集。基于该假设，本项目拟通过测定不同粒级团聚体δ13C和δ15N值，结合土壤团聚体呼吸和有机氮矿化过程，确定团聚体有机质周转过程中碳氮同位素分馏；分析不同年龄有机质在土壤团聚体中分布状况，定量各团聚体对土壤碳排放和供氮能力的贡献，明确碳氮元素在各团聚体及有机质组分间可能的流动通道，阐明碳氮元素在团聚体中迁移和转化过程。本项目基于13C或15N稳定同位素技术研究土壤团聚体碳氮动态，其结果可丰富土壤团聚体理论。

土壤团聚体周转过程是土壤发育的关键过程，其通过抑制颗粒有机物的分解和矿物颗粒的相互作用促进有机质固定。有机质固定导致碳稳定同位素分馏，使不同组分中δ13C值多样化。其可能原因是，土壤微生物对有机质利用分解利用过程中, 轻同位素优先分解，残留在土壤中的重同位素比例增加。据此假设：土壤团聚体有机质周转会造成碳同位素分馏，且13C同位素随着时间从大团聚体向微团聚体富集。基于该假设，本项目通过测定不同粒级团聚体δ13C值，结合土壤团聚体呼吸和有机质矿化过程，研究了团聚体有机质周转过程中碳同位素分馏效应，以及不同年龄有机质在土壤团聚体中分布状况，分析了碳元素在各团聚体及有机质组分间可能的流动通道，以及碳元素在团聚体中迁移和转化过程。研究获得以下主要结论：.确证了土壤团聚体周转过程中的碳稳定同位素分馏，其分馏效应可达6 ‰，13C同位素从大团聚体向微团聚体富集。基于这种同位素分馏效应，分析了C元素在各团聚体及有机质组分间可能的流动通道，发现了土壤团聚体中碳元素由大团聚体向小团聚体迁移的稳定同位素证据，并明确了不同土壤团聚体碳新老分布及更新特征，本研究是基于13C自然丰度稳定状态下研究碳流动的方法，研究结果可丰富土壤团聚体理论。.应用土壤团聚体周转及其固碳理论，阐明了土壤有机氯污染物在团聚体系统中的赋存特征与输移过程。发现了有机氯污染物不同代谢物在不同粒径团聚体中分布出现分异的现象，并分析了其与土壤团聚体有机质周转的关系，明确有机氯污染物在土壤中的环境行为与土壤团聚体周转过程密切关联。研究结果为准确评价土壤有机氯污染物的环境风险提供支持。