The effect of soil pH and phosphorus interactions on nitrous oxide emissions and microbial communities involved in nitrogen cycling

Excess application of Nitrogen (N) to agricultural soils can lead to environmental pollution. As nitrous oxide (N2O) is a potent greenhouse gas, it is of critical importance to reduce its emission for climate change mitigation. Availability of nitrogen can facilitate denitrification, an anaerobic respiratory pathway carried out by microbial communities in which N2O is an intermediate product. An understanding of soil, climatic and edaphic factors influencing microbial communities and their activity is key to reducing N2O emissions. Soil pH strongly impacts microbial community structure, with a direct effect on NosZ, the pH-sensitive enzyme catalysing N2O reduction. We thus expect that microbial communities in acidic soils have a reduced capacity to mitigate N2O emissions. It is likely that other management factors, like phosphorus application, interact with pH; causing changes to chemical nutrient availability and direct effects on microbial composition. The complexity linking N2O emissions and microbial activity (impacted by soil pH), and the interacting role phosphorus availability plays in this relationship, is not yet understood. In this study, the capacity of microbial communities to denitrify, as well as the functional microbial community impacted by soil pH, were analysed by potential denitrification assays, measuring N2O fluxes and N2O/(N2O+N2) ratios; and qPCR analysis of denitrification genes. This was investigated across two soil types with a pH gradient and range of phosphorus application rates. Understanding the link between the microbial communities and N2O production can be applied in agricultural management to reduce emissions from fields.