Abstract：
Algal extracellular organic matter (EOM) metabolites exert considerable impact on the carbon (C), nitrogen (N), and phosphorus (P) cycles mediated by attached bacteria. Field investigations were conducted in two ponds to explore the relationship among EOM metabolites from Microcystis and Dolichospermum, co-occurring microbes, and nutrient recycling from April 2021 to December 2021. Microcystis blooms primarily produced more complex bound EOM (bEOM) metabolites with many amino acid components, which facilitated bacterial colonization and provided sufficient substrates for ammonification. Meanwhile, high abundances of dissimilatory nitrate reduction to ammonium genes from co-occurring microbes such as Rhodobacter have demonstrated their strong N retention ability. Metabolic products of bEOM from Microcystis comprise a large number of organic acids that can solubilize non-bioavailable P. All these factors have collectively resulted in the increase of all fractions of N and P, except for nitrate (NO3--N) in the water column. In contrast, the EOM metabolite from Dolichospermum was simple, coupled with high abundance of functional genes of α-glucosidase, and produced small molecular substances fueling denitrification. The metabolic products of EOM from Dolichospermum include abundant N-containing substances dominated by heterocyclic substances, suggesting that the metabolic products of Dolichospermum are not conducive to N regeneration and retention. Therefore, the metabolic products of EOM from Microcystis triggered a shift in the attached microbial community and function toward C, N, and P recycling with close mutual coupling. Acquisition of N and P in Dolichospermum is dependent on itself based on N fixation and organic P hydrolysis capacity. This study provides a new understanding of the contribution of algal EOM to the nutrient cycle.
摘要：
藻类细胞外有机物（EOM）代谢产物对碳（C）产生相当大的影响，氮(N),和磷（P）循环由附着细菌介导。在两个池塘中进行了实地调查，以探索微囊藻和Dolichospermum的EOM代谢产物之间的关系，共存的微生物，和营养回收从2021年4月到2021年12月。微囊藻主要产生具有许多氨基酸成分的更复杂的结合EOM（bEOM）代谢物，这促进了细菌定植并为氨化提供了足够的底物。同时,从共存的微生物如红杆菌属中大量的异化硝酸盐还原成铵基因已经证明了它们强大的N保留能力。来自微囊藻的bEOM的代谢产物包含大量的有机酸，这些有机酸可以溶解非生物可利用的P。所有这些因素共同导致N和P的所有分数增加，除了水柱中的硝酸盐(NO3--N)。相比之下,来自Dolichospermum的EOM代谢物很简单，加上高丰度的α-葡萄糖苷酶功能基因,并产生小分子物质作为反硝化的燃料。Dolichospermum的EOM的代谢产物包括以杂环物质为主的丰富的含氮物质，表明Dolichospermum的代谢产物不利于N的再生和保留。因此,来自微囊藻的EOM的代谢产物引发了附着的微生物群落和功能向C的转变，N,和P回收具有紧密的相互耦合。基于N固定和有机P水解能力，Dolichospermum中N和P的获取取决于自身。这项研究为藻类EOM对营养循环的贡献提供了新的认识。
