Increased microbial and substrate complexity result in higher molecular diversity of the dissolved organic matter (DOM) pool

Marine dissolved organic matter (DOM) represents one of the largest reduced carbon pools on Earth. Diverse microbial metabolic activities play important roles in shaping this pool. But the interactions between the complexity of DOM substrates and microbial communities and its influence on the microbial produced DOM remain poorly understood. In this study, we investigated how the addition of substrates with different complexity (glucose, laminarin and Synechococcus-derived DOM) impacted the production of new DOM by an individual opportunist Alteromonas strain and a coastal natural microbial community. Our experiments reveal that the microbial complexity was more important than the substrate in shaping the molecular composition of DOM. Further, our results showed that the DOM composition played a larger role in shaping the microbial compositions than the concentrations of DOM and inorganic nutrients. Combined our network analysis revealed that complex substrates resulted in higher molecular diversity of the microbial produced DOM, sustained a higher microbial diversity, and maintained a more diverse association between microbial communities and DOM molecules. Overall, the present study indicate that the microbial diversity contributes to DOM molecular diversity and vice versa, highlighting the importance of microbial-substrate interactions in shaping the marine DOM pool.海洋溶解有机质（dissolved organic matter, DOM）是地球上最大的还原性碳库之一。多样的微生物代谢活动在塑造该碳库的过程中发挥着关键作用。然而，目前人们对DOM底物复杂性与微生物群落之间的相互作用，及其对微生物产生的溶解有机质的影响仍知之甚少。本研究探究了添加不同复杂性底物（葡萄糖、昆布多糖及聚球藻衍生的DOM）对一株机会性交替单胞菌菌株及沿海天然微生物群落产生新DOM的影响。实验结果表明，相较于底物类型，微生物群落复杂性对DOM分子组成的塑造作用更为显著。进一步研究发现，相较于DOM浓度与无机营养盐水平，DOM组成对微生物群落组成的塑造作用更强。结合本研究的网络分析结果可知，复杂底物可提升微生物产生的DOM的分子多样性，维持更高的微生物多样性，并强化微生物群落与DOM分子间的多样关联。综上，本研究表明微生物多样性有助于提升DOM的分子多样性，反之亦然，凸显了微生物-底物相互作用在塑造海洋DOM库中的重要意义。