The imbalance between NO production and reduction by multi-microbial communities determines sedimentary NO emission potential in the Pearl River Estuary.

Denitrification is the dominant process of nitrogen removal and nitrous oxide (NO) emissions in estuarine ecosystems. However, little is known regarding the microbial mechanism of the production and reduction of NO in estuaries. We investigated in situ dissolved NO as well as potential NO production rate (NPR), reduction rate (NRR), and emission rate (NER), and key functional genes related to NO transformation of denitrification in the Pearl River Estuary. Higher NO emission potential was found in the upstream and midstream regions with higher NPR and lower NRR values. In contrast, higher NRR values were detected in downstream. Notably, nirS and nirK type NO producers dominated the upstream zone, whereas abundant NO reducers, especially nosZ II type NO reducers, were observed in downstream. Most importantly, the gene abundance ratio (R) was significantly correlated with the NO emission potential (R). Niche differentiation between NO producers and NO reducers from upstream to downstream affected NO emission potential. This study highlights the NO emission potential in estuarine sediments is determined by an imbalance between NO production and the reduction of multi-bacterial communities.