Thermodynamic sensitivity of ammonia oxidizers-driven NO fluxes under oxic-suboxic realms.

In terrestrial ecosystems, the nitrogen dynamics, including NO production, are majorly regulated by a complex consortium of microbes favored by different substrates and environmental conditions. To better predict the daily, seasonal and annual variation in NO fluxes, it is critical to estimate the temperature sensitivity of different microbial groups for NO fluxes under oxic and suboxic conditions prevalent in soil and wetlands. Here, we studied the temperature sensitivity of two groups of ammonia oxidizers, archaea (AOA) and bacteria (AOB), in relation to NO fluxes through both nitrification and nitrifier-denitrification pathways across a wide temperature gradient (10-55 °C). Using square root theory (SQRT) and macromolecular rate theory (MMRT) models, we estimated thermodynamic parameters and cardinal temperatures, including maximum temperature sensitivity (T). The distinction between NO pathways was facilitated by microbial-specific inhibitors (PTIO and CH) and controlled oxygen supply environments (oxic: ambient level; and suboxic: ∼4%). We found that nitrification supported by AOA (Nt) and AOB (Nt) dominated NO production in an oxic climate, while only AOB-supported nitrifier-denitrification (ND) majorly contributed (>90%) to suboxic NO budget. The models predicted significantly higher optimum temperature (T) and T for Nt and ND compared to Nt. Intriguingly, both Nt and ND exhibited significantly wider temperature ranges than Nt Altogether, our results suggest that temperature and oxygen supply control the dominance of specific AOA- and AOB-supported NO pathways in soil and sediments. This emergent understanding can potentially contribute toward novel targeted NO inhibitors for GHG mitigation under global warming.