“微生物泵”作用下土壤有机质的稳定及其对憎水性有机污染物的不可逆吸附

Soil organic matter (SOM), especially the relatively stable organic matters, is of great importance in controlling the sorption and sequestration of hydrophobic organic contaminates (HOCs) in the environment. The stable SOM was traditionally considered as biochemically resistant polymers, which was originated from plant residues, such as lignin. However, recent studies found that the stability of these complex polymers seems to be overestimated, which just contributed to the short-term stabilization of SOM. Whereas an increasing number of evidence suggests that microbial-derived carbon, such as microbial necromass, plays a significant role in SOM stabilization and these stable SOM are essential for controlling the sequestration of HOCs in a long-term. This microbial-derived carbon is the metabolites and residues of microorganism and this microorganism-mediated process is referred to as “microbial carbon pump” (MCP). The formation and stabilization of SOM produced by MCP are dependent on quality of substrates, microbial communities (fungal and bacterial groups) and mineral. However, it remains largely unknown how interaction among these factors impacts SOM formation impacts SOM formation and stabilization. Therefore, understanding the interaction mechanisms between stable SOM produced by MCP and HOCs will provide a new insight for irreversible adsorption and risk evaluation of HOCs. Therefore, this study is specifically designed to investigate the stabilization of SOM through MCP and their interactions with HOCs, especially the irreversible sorption. Seven substrates (a series of simple to complex organic molecules) will be separately mixed with three different minerals (kaolinite, montmorillonite and hematite) to cultivate and simulate the formation of SOM under MCP. The stabilization mechanism of SOM under MCP process as affected by mineral properties will be systematically investigated. The change of microbial community during the different input of various substrates will also be examined to explain SOM formation and stabilization. In addition, the interactions between SOM produced by MCP and HOCs will be systematically studied. The apparent nonlinear index, desorption release coefficient and thermodynamics irreversible coefficient will be introduced to describe the correlation between HOCs irreversible adsorption and SOM property in detail. This line of study will provide more evidence for SOM stability under MCP and a new viewpoint to understand long-term HOCs sequestration and environmental risks.

土壤有机质（SOM），特别是其相对稳定的组分，是控制憎水性有机污染物（HOCs）吸附稳定的关键因素。最近的研究指出，“微生物泵”作用下的SOM（即微生物介导下的有机质再合成产物）对稳定性碳库有重要贡献，打破了以植物衍生物碳复杂分子结构为主导的稳定性碳库的传统观点。理解“微生物泵”作用下的稳定SOM与HOCs的相互作用成为环境地学研究的新挑战。本项目拟首先构建不同的基质和矿物条件下，在“微生物泵”作用下形成的SOM，研究其形成和稳定机制；初步阐释微生物-基质不同组合下的微生物群落组成变化对SOM形成的调控；系统研究“微生物泵”作用下形成的SOM与HOCs的相互作用，引入表观非线性指数、解吸释放系数、热力学不可逆指数等，重点描述HOCs的不可逆吸附与SOM性质的关联性。本研究将为“微生物泵”作用下的SOM稳定提供更为系统的证据，并从一个新的角度理解HOCs的长期锁定及环境风险。

稳定性有机碳是控制污染物尤其是憎水性有机污染物吸附稳定的关键组分。近年来，“微生物碳泵”作用下的微生物残体碳对稳定性碳库有重要贡献，打破了以植物衍生物碳复杂分子结构为主导的稳定性碳库的传统观点。然而，”微生物碳泵“作用下SOM形成和稳定及其对污染物相互作用仍不明确。本项目通过添加了不同分子结构碳源（甘氨酸、葡萄糖以及2，6-二甲氧基苯酚）于蒙脱石/赤铁矿与石英混合矿物进行长期培养形成微生物残体有机质，重点研究不同碳源与矿物作用下微生物残体碳的组分及其稳定性机制，揭示了微生物残体碳主要来源于真菌残体，与活体微生物量无明显关系；随着碳源结构的复杂性增强，其形成的残体碳的稳定性越强。此外，蒙脱石较赤铁矿对微生物残体碳的抗化学氧化性更强。同时，矿物的存在抑制了细菌残体碳的释放累积量，然而，矿物的存在增加了真菌残体碳的碳释放累积量，其中蒙脱石更为显著。此外，本研究发现了PHE在赤铁矿组残体碳的吸附能力主要取决于赤铁矿的结构，随着覆盖的残体碳越多，反而阻碍PHE的吸附；而蒙脱石组残体碳对PHE的吸附不仅依赖于蒙脱石的比表面积，更依赖于微生物残体碳的性质。然而，残体碳吸附PHE后，其发现了明显的解吸现象，残体碳对PHE的解吸释放量RR远高于纯矿物，其中碳源结构越复杂形成的残体碳对PHE的解吸释放量越低。反之，残体碳对重金属Pb(Ⅱ)的吸附能力强，非线性吸附指数n普遍低于0.5，表明对Pb(Ⅱ)吸附的非线性强，且细菌残体的异质性高于真菌残体。此外，其吸附解吸滞后性很高，RR普遍低于0.1，且赤铁矿/真菌残体碳的滞后性高于赤铁矿。以上结果表明，微生物残体与矿物作用更有利于吸附固定重金属,而对疏水性有机污染物的固定很弱尤其是赤铁矿形成下的微生物残体。本研究为微生物残体碳的稳定提供了更系统的证据，且为评价土壤修复治理提供理论基础。