Impacts of Biostimulants on Nitrous Oxide Emissions and the Soil Microbiome

ABSTRACT Background Overapplication of nitrogenous fertilizer and enhanced microbial activity in agricultural soils are drivers of increasing greenhouse gas emissions. Plant biostimulants are products applied to crops to improve nutrient use efficiency or applied to soil to enhance the cycling of nutrients. Aims We wanted to know if treating the soil environment with biostimulants while applying nitrogen fertilizer influences nitrous oxide (N 2 O) emissions. Methods We incubated cultivated soil with high nitrogen, low nitrogen, and low nitrogen with different biostimulants (bacteria, protein hydrolysate, or a seaweed extract) in lab bottles and measured greenhouse gas emissions over 10 days. We also employed 16S and ITS amplicon sequencing to determine changes in the soil microbiome. Results Reducing nitrogen fertilizer significantly decreased cumulative nitrous oxide emissions, except when biostimulants were applied. This biostimulant‐induced increase in N 2 O is likely due to higher potential net nitrogen mineralization, as reflected by a low net loss in soil ammonium levels after the experiment. The application of protein hydrolysate and bacterial biostimulants reduced fungal richness. Conclusions Biostimulants can increase nitrous oxide emissions in soils with high water‐filled pore space. When applying bacteria‐ or protein hydrolysate‐based biostimulants, it is crucial to consider the population dynamics of native microorganisms in the target area, as antagonistic interactions may arise.