Nitrate Exposure: A Metric to Describe the Influence of Soil NO3- On N2 O Emissions.

Nitrate (NO₃^-) is a pivotal aspect of the soil biological environment. It represents an important nutrient in biosynthesis, a terminal electron acceptor in anaerobic respiration, and a mobile anion. Because of nitrate’s dynamic nature, NO₃^- concentrations frequently exhibit extreme spatial and temporal variability.  Further the influence of NO₃^- on N₂O emissions is also variable in time and may be temporally shifted as a result of impacts of NO₃^- on denitrifier populations or gene expression.  Spatial variability of NO₃^- and its influence on denitrification result in poor correlation between processes such as N₂O emissions and point-in-time measurements of NO₃^- concentration. We examined the utility of a new parameter, NO₃^- exposure (NE), to represent the influence of nitrate on N₂O emissions. The spatial and temporal integration of measurements of NO₃^- concentration better correlated with cumulative N₂O emissions than point-in-time measurements. This observation points to NE as an emergent property reflecting not only the proximal effect of NO₃^- on a biochemical reaction such as N₂O production, but also the more distal processes that control these reactions, enzymes and microbial communities.