Mitigated N₂O emissions from submerged-plant-covered aquatic ecosystems on the Changjiang River Delta

Submerged plants affect nitrogen cycling in aquatic ecosystems. However, whether and how submerged plants change nitrous oxide (N₂O) production mechanism and emissions flux remains controversial. Current research primarily focuses on the feedback from N₂O release to variation of substrate level and microbial communities. It is deficient in connecting the relative contribution of individual N₂O production processes (i.e., the N₂O partition). Here, we attempted to offer a comprehensive understanding of the N₂O mitigation mechanism in aquatic ecosystems on the Changjiang River Delta according to stable isotopic techniques, metagenome-assembly genome analysis, and statistical analysis. We found that the submerged plant reduced 45 % of N₂O emissions by slowing down the dissolved inorganic nitrogen conversion velocity to N₂O in sediment (V_f-[DIN]_sed). It was attributed to changing the N₂O partition and suppressing the potential capacity of net N₂O production (i.e., nor/nosZ). The dominated production processes showed a shift with increasing excess N₂O. Meanwhile, distinct shift thresholds of planted and unplanted habitats reflected different mechanisms of stimulated N₂O production. The hotspot zone of N₂O production corresponded to high nor/nosZ and unsaturated oxygen (O₂) in unplanted habitat. In contrast, planted habitat hotspot has lower nor/nosZ and supersaturated O₂. O₂ from photosynthesis critically impacted the activities of N₂O producers and consumers. In summary, the presence of submerged plants is beneficial to mitigate N₂O emissions from aquatic ecosystems.