TEMPORARY REMOVAL: Growing grass reduces soil N2O emissions and stimulates proliferation of denitrifying bacteria

Abstract Nitrogen (N) fertilization is the major contributor to nitrous oxide (N2O) emissions from agricultural soil. Previous studies have established that perennial grasses, barley, maize and other plants increase denitrification rates in soil. However, the majority of investigations of soil N2O emissions have been conducted without plants. The aim of this study, therefore, was to investigate how the presence of a perennial grass affects soil N2O emissions and denitrifier community size. To achieve this, a microcosm experiment was conducted with soil planted with perennial ryegrass (Lolium perenne L.) and bare soil, each with four levels of fertilizer (0, 5, 10 and 20 g N m−2; applied as calcium ammonium nitrate). The closed-chamber approach was used to measure soil N2O fluxes. Real-time PCR was used to estimate the biomass of bacteria and fungi and the abundance of genes involved in denitrification in soil. The results showed that the presence of ryegrass decreased the nitrate content in soil, as compared to bare soil, while no effect on dissolved organic carbon was observed. Cumulative N2O emissions of soil with grass were lower than in bare soil at 5 and 10 g N m−2 fertilization, but statistically indistinguishable in soil without fertilization and with 20 g N m−2. Fertilization did not affect the abundance of soil bacteria and fungi. Soil with grass showed greater abundances of bacteria and fungi, as well as microorganisms carrying narG, napA, nirK, nirS and nosZ clade I genes. It is concluded that growing perennial ryegrass can reduce soil N2O emissions and promote denitrifier community size compared to bare soil. This highlights the importance of plant cover for the reduction of N2O emissions from soil, particularly during N fertilization. Future research should explore how different plants species and communities affect denitrifying communities in soil.