Distinct N-cycling microbial communities contribute to microtopographic variation in soil nitrous oxide emissions
Ponded area within an agricultural field in central Illinois
Climate change is increasing the frequency and intensity of large precipitation events that flood soils and establish oxygen deficient conditions that promote microbial denitrification. Denitrification is a process that reduces nitrogen compounds to nitrogen containing gases through enzyme-driven processes. This contributes to the release of N2O, a greenhouse gas and may be favored within topographic depressions in otherwise flat fields that are prone to ponding, which establishes “hotspots” of N2O emissions.
Rainfall can also stimulate N2O emissions from nearby upslope areas and suppress N2O from depressional areas, causing the location of N2O hotspots to change with environmental conditions. The location of N2O hotspots may also depend on the distribution of soil microbial communities that are responsible for the production and consumption of N2O in soils.
Relating soil microbial community composition to N2O emissions remains challenging. To see how spatial variation in soil microbial communities impacts N2O emissions, researchers measured the community composition of active microorganisms using nitrogen cycling based DNA sequencing. They used stable nitrogen isotope tracers to relate microbial communities to process rates and found that the diversity of microbial taxa with genes that produce N2O and N2 were correlated with N2O emissions from denitrification. Depressional soils had more diverse active N2O consuming communities under flooded conditions, limiting net N2O emissions compared to upslope soils.
These results show that depressional soils maintain distinct microbial communities that likely promote higher rates of N2O reduction compared to upslope soils. Soil microtopography can, therefore, select for distinct microbial communities that emit different amounts of N2O in response to large precipitation events.
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