河道藻源胞内有机质光化学-生物降解机制

藻细胞破裂后会向水体释放大量的胞内有机质 (intracellular dissolved organic matter, I-DOM) 。I-DOM在河道中将经历复杂的光降解和生物降解过程，影响其在河道中的迁移转化和环境效应。为了探明光照和微生物对I-DOM的降解机制，开展了光降解、生物降解和光-生物降解实验。结果表明，I-DOM经7 d光降解和生物降解后，溶解性有机碳 (dissolved organic carbon, DOC) 的去除率分别为70%和81%；虽然光照1 d能去除38%的DOC，但后续生物降解 (光-生物降解) 与无光照生物降解对DOC的去除效率一致。进一步的研究表明，生物降解过程中的呼吸商 (respiratory quotient, RQ) 低于光-生物降解过程，说明相比于生物降解过程，光-生物降解过程中经光照后生物呼吸时所利用I-DOM的性质发生了改变，进而影响了生物呼吸时O₂的消耗和CO₂的产生。生物降解过程中微生物主要利用原始的I-DOM分子；而在光-生物降解过程中，生物降解过程的微生物主要利用经光降解转化后的I-DOM分子。光-生物降解过程中，光照消耗了I-DOM中可生物降解的脂质、蛋白质和木质素类组分，导致I-DOM的生物降解效率降低；同时，光照将I-DOM中的大分子物质分解成高O/C的小分子物质，使微生物代谢需要的O₂减少，小分子物质则更易被生物降解矿化生成CO₂，导致RQ升高。本研究结果可为河道水质调控提供参考。

Photochemical-biodegradation mechanism of intracellular dissolved organic matter from river algae

The rupture of algal cells leads to the release of a significant amount of intracellular dissolved organic matter (I-DOM) into the aquatic environment. I-DOM undergo complex photodegradation and biodegradation processes in river, affecting its migration, transformation and environmental effects. To investigate the degradation mechanism of I-DOM by irradiation and microorganisms, photodegradation, biodegradation, and photo-biodegradation experiments were conducted. The results showed that after 7 days of photodegradation and biodegradation, the removal rates of dissolved organic carbon (DOC) of I-DOM were 70% and 81%, respectively. Although irradiation for one day can remove 38% of DOC, the subsequent biodegradation (photo-biodegradation) removal efficiency of DOC was the same as that of non-irradiation biodegradation. Further research showed that the respiratory quotient (RQ) during biodegradation process was lower than during photo-biodegradation process, indicating that compared with the biodegradation process, the properties of I-DOM used by microbial respiratory after irradiation in the photo-biodegradation process changed, further affecting the consumption of O2 and the production of CO2 during biological respiration. In the process of biodegradation, microorganisms mainly used the original I-DOM molecules, while in the process of photo-biodegradation, microorganisms mainly used the I-DOM molecules transformed by photodegradation. In the process of photo-biodegradation, irradiation consumed the biodegradable lipid, protein and lignin components in I-DOM, resulting in a decrease in the biodegradation efficiency of I-DOM. At the same time, irradiation decomposes high molecular weight I-DOM into low molecular weight I-DOM with high O/C, reducing the O2 required for microbial metabolism. The low molecular weight substances were more likely to be biodegraded and mineralized to produce CO2, resulting in a significant increase in RQ. This study contributes to our understanding of the migration and transformation of I-DOM in rivers and provides reference for water quality control.