水环境中秸秆源溶解有机质的组成及光化学活性特征

利用紫外-可见吸收光谱、三维荧光光谱和稳态光化学反应技术，对水环境中水稻和小麦秸秆短期（91d）分解释放的溶解有机质（DOM）的组成、结构和光化学活性进行了研究.结果表明：在水环境中，秸秆分解释放DOM过程可分为物理淋溶、易分解组分分解和难分解组分分解三个阶段，其中易分解组分是该分解过程中秸秆DOM的主要来源；随分解周期增长，秸秆源DOM的芳香性、腐殖化程度及分子量不断增大，而生物可利用性逐渐减小；秸秆源DOM中的类酪氨酸、类腐殖酸和类富里酸在秸秆分解过程中逐渐累积，至分解末期，3种组分在水稻和小麦秸秆DOM中的含量分别增加了4.2%~14.3%和5.9%~12.8%，而类色氨酸和溶解性微生物分泌物相对不稳定，会被逐渐分解；秸秆源DOM的紫外和荧光光谱特征指数SUVA₂₅₄、E2/E3、S_275~295、S_R、BIX和FI均与其光生HO×、¹O₂和三线态DOM间具有良好的相关关系（r > 0.61，P < 0.05），因此秸秆源DOM的光化学活性由其芳香结构、分子量及生物可利用性共同决定.鉴于此，研究认为，探讨生物可利用组分的光化学活性，及构建光谱特征指数预测DOM光化学活性的数学模型，是今后秸秆源DOM生态环境作用研究的两项重要内容.

Compositional characteristics and photochemical activity of dissolved organic matter derived from straw in aquatic environment

Dissolved organic matter (DOM) was extracted from rice and wheat straw at different decomposition phases in aquatic systems. The component, structure and photochemical activity of the DOM were characterized by UV-vis absorption spectroscopy, three-dimensional fluorescence spectroscopy and static photochemical reaction methods. Results showed that decomposition process of straw concluded three phases, i.e., physical-leaching, vulnerable and refractory component decomposition, and the vulnerable decomposition component was the main source of the DOM. The aromaticity, humification degree and molecular weight of the straw-derived DOM increased as a function of decomposition time, while the bioavailability of the DOM gradually decreased. The tyrosine-, humic acid- and fulvic acid-like substances of the DOM gradually accumulated during the decomposition period. By the end of decomposition, the contents of the three components in rice and wheat straw-derived DOM increased by 4.2%~14.3% and 5.9%~12.8%, respectively. However, the tryptophan-like substance and soluble microbial secretion were relatively unstable and gradually decomposed. The UV and fluorescence spectral indices SUVA₂₅₄, E2/E3, S_275~295, S_R, BIX and FI were strongly correlated to the photochemically generated HO×, ¹O₂ and triplet-state DOM (r > 0.61, P < 0.05). Therefore, the photochemical activity of the DOM was concurrently dominated by its aromaticity, molecular weight and bioavailability. Based on the results, it is suggested that exploring photochemical activity of bioavailable components and constructing mathematical models for predicting photochemical activity of DOM should be strengthened in the future studies, which is helpful for understanding the ecological significance of straw-derived DOM.