Soil N2O emission potential falls along a denitrification phenotype gradient linked to differences in microbiome, rainfall and carbon availability

Abstract

Soil denitrification produces the potent greenhouse gas nitrous oxide (N2O) and by further reduction of N2O, the harmless inert gas N2. N2O emission is determined by rate and timing of the N2O producing and reducing steps which are sensitive to a series of proximal and distal regulators such as pH and microbial community composition. Microbial community associations to N2O emission potential (N2O/(N2O + N2)) are commonly entangled with pH leaving the true role of community composition unclear. Here, we leverage a set of soil microbiomes strongly linked to rainfall above pH to test the hypothesis that microbiome vs. N2O emission potential (N2O/(N2O + N2)) correlations will be maintained across alternative distal drivers. N2O emission potential (N2O/(N2O + N2)) and denitrification gas (NO, N2O, N2) kinetics were assessed by automated gas chromatography while community composition was assessed by 16 S rRNA gene sequencing and qPCR of nosZI and II genes. Analyses revealed a sustained correlation between microbiome and N2O emission potential (N2O/(N2O + N2)) in the absence of a pH effect. Further, a continuum of gas accumulation phenotypes linked to NO accumulation and sensitive to carbon addition are identified. Separate phenotypes carried out N2O production and reduction steps more concurrently or sequentially and thus determined N2O accumulation and emission potential (N2O/(N2O + N2)). Concurrent N2O producing/reducing soils typically contained NO accumulation to a low steady state, while carbon addition manipulations which increased NO accumulation also increased sequentiality of N2O production/reduction and thus emission potential (N2O/(N2O + N2)). These features may indicate a conserved NO inhibitory mechanism across multiple effectors (rainfall, community composition, carbon availability).