森林源溶解性有机质分子水平化学特性及其对氮沉降响应

The chemical composition and stability of the forest-derived dissolved organic matter (DOM) play critical roles in the carbon cycling in the watershed. However, the molecular composition and stability of the forest-derived DOM as well as their responses to the rapidly increasing nitrogen deposition in China are not well understood. Complementary molecular-level approaches are desirable to comprehensively depict the DOM characteristics and their responses to nitrogen deposition with high analytical sensitivity and high resolution. To elucidate the DOM composition and its response to N deposition, the proposed project will combine non-targeted (including fluorescence spectroscopy, nuclear magnetic resonance spectroscopy, and high-resolution mass spectrometry) and targeted analyses (biomarker analyses) to analyze the seasonal variations in DOM chemistry in throughfall, stemflow, surface runoff, lysimeter samples from a subtropical forest receiving different levels of nitrogen deposition. To understand the DOM stability and its response to nitrogen deposition, we will conduct individual and interactive photochemical and microbial degradation experiments on DOM of different sources. The outcome of this project will significantly advance the knowledge of the molecular composition and stability of forest-derived DOM and provide new insight in the response of coupled carbon and nitrogen cycling to the increasing global nitrogen deposition.

森林源溶解性有机质（DOM）的化学构成与稳定性对流域系统中的碳循环起关键作用，然而这些化学特性及其对氮沉降快速增加的响应趋势尚未明确。互补性分子水平方法因综合全面、高灵敏度和高分辨率等优势，可以系统地剖析森林内长时序多来源DOM的化学特性及其对氮沉降响应。本项目拟以我国高氮沉降、高储碳的亚热带森林为对象，采用基于光谱、核磁谱与高分辨质谱的非目标性手段，结合基于分子标记物的目标性手段，对不同氮沉降处理下样地中林冠穿透水、树干径流、地表径流和壤中流的化学特性的季节性变化进行分析，从分子水平揭示森林源DOM的构成及其对氮沉降响应。同时，我们将通过室内严格控制的单一和交互性光化学与微生物降解实验，揭示森林源DOM的降解稳定化机理及其对氮沉降响应。本项目成果将深化对森林源DOM分子结构和稳定性的认识，为全球氮沉降情形下碳氮循环的耦合机制提供新认识。

森林源溶解性有机质（DOM）的化学构成与稳定性对陆地碳循环起关键作用，然而这些化学特性及其对氮沉降的响应尚未明确。本项目以我国高氮沉降、高储碳的亚热带森林为主要研究对象，并结合美国温带落叶森林的长期氮添加实验台站为辅助对象，采用互补性分子水平方法，从分子水平揭示森林源DOM的构成及其对氮沉降响应。研究表明， DOM特征随土壤深度发生显著变化，并且豆科植物和非豆科植物人工林之间存在显著差异。在土壤渗透过程中，微生物来源的DOM（蛋白质样成分和类脂化合物）增加，但植物来源的DOM（碳水化合物和植物多酚）减少。此外，氮添加人工林大大增加了豆科人工林中高质量分子和浓缩芳香类化合物的积累。室内降解处理显著改变了DOM的光谱特征和分子结构。林冠穿透水和树干径流中的DOM与地表径流和壤中流中的DOM在不同的降解处理中具有不同的响应。所有来源的DOM的光降解程度均大于生物降解，表明光化学作用在森林源DOM的降解过程中占主导地位。对于温带森林而言，其土壤DOM对长期氮沉降的响应远高于森林土壤碳储量的响应，DOM化学性质及其氯化反应性显著改变，但并未产生毒性更大的消毒副产物，未增加饮用水安全的额外风险。本项目成果深化了对森林源DOM分子结构和稳定性的认识，为全球氮沉降情形下碳氮循环的耦合机制提供了新认识。