How Benzoic Acid—Driven Soil Microorganisms Influence N2O Emissions

Urine-derived and plant-derived benzoic acid can accumulate within soil, and it likely changes the soil microbial community as well as N2O emissions; however, its mechanism is not clear. This study conducted an incubation experiment to monitor N2O emissions under low moisture (40% water-filled pore space (WFPS)) and high moisture (85% WFPS) conditions. Metagenomic sequencing and q-PCR methods were used to determine the link between N2O emissions and the composition and functions of soil microbiota. Benzoic acid (BA) was found to significantly, yet dose-dependently, impact N2O emissions; that is, low BA concentrations increased N2O, whereas high BA decreased N2O. However, this was only found under high moisture conditions. In contrast, BA had little impact on N2O emissions under low moisture conditions. Under high moisture conditions, BA increased the gene copy number of bacteria and fungi, and decreased the ratio of bacteria to fungi. Similarly, BA significantly increased the abundance of denitrification functional genes, but reduced the (NirS + NirK)-to-NosZ ratio at the peak of emission. This is in agreement with the observation of the increased relative abundance of genes encoding N2O reductase (EC 1.7.2.4) and NO3− heterotrophic reductase (EC 1.7.1.15, EC 1.7.2.2) in the metagenomic analysis. In summary, high concentrations of benzoic acid reduce N2O emissions by promoting the reduction of N2O. This study revealed the impact of BA on soil microbiota and highlighted the favorable conditions and underlying mechanism behind BA’s significant impact on soil N2O emissions. This study’s novelty lies in the fact that it deepens our understanding of the complicated role of root exudates and metabolites of animals and plants in soil.