Effect of conversion of brackish marshes to aquaculture ponds on comammox Nitrospira communities in the Min River Estuary. metagenomes

Sediment ammonia oxidation from aquatic ecosystems plays a critical role in global nitrogen cycle, including nitrous oxide (N2O) emissions. Conversion of coastal marshes to aquaculture ponds has been frequently shown to significantly influence N2O emissions, but the corresponding effect on ammonia oxidation and ammonia-oxidizing microorganisms remains elusive. Here, we compared the newly discovered complete ammonia oxidation (comammox, CMX) abundance and community structure, and potential ammonia oxidation rate between brackish marshes and the nearby converted shrimp aquaculture ponds in Southeast China over a 10-month period. We hypothesized that aquaculture reclamation would decrease the abundances of AOA, AOB and CMX Nitrospira and potential ammonia oxidation rate due to a decrease in oxygen and substrate supply. We also hypothesized that temporal variations in ammonia oxidizer abundance and ammonia oxidation potential would be stronger in the marsh, thanks to its more exposed environment, than in the aquaculture ponds. The results would advance our understanding of how seasons and landscape change impact ammonia oxidizer communities and ammonia oxidation in coastal areas.

水生生态系统沉积物中的氨氧化作用在全球氮循环中发挥关键作用，该过程同时涉及一氧化二氮（N₂O）的排放。已有研究表明，滨海湿地转为水产养殖池塘的土地利用转变，会显著影响N₂O排放，但该过程对氨氧化作用及氨氧化微生物的相应影响仍不明晰。本研究于中国东南部的咸淡水湿地及其邻近的转用虾塘开展了为期10个月的采样分析，对比了二者之间新发现的完全氨氧化作用（comammox, CMX）的丰度、群落结构以及潜在氨氧化速率。本研究提出两项假说：其一，水产养殖垦殖会因氧气与底物供给减少，导致氨氧化古菌（AOA）、氨氧化细菌（AOB）以及CMX硝化螺菌的丰度与潜在氨氧化速率下降；其二，相较于水产养殖池塘，咸淡水湿地的环境更为开放，其氨氧化微生物丰度与氨氧化潜力的季节动态变化幅度会更为显著。本研究结果将有助于深化我们对季节变化与土地景观转变如何影响滨海区域氨氧化微生物群落及氨氧化作用的认知。