Reductions in nitrous oxide emissions in diverse crop rotations linked to changes in prokaryotic community structure

Abstract

Diverse crop rotations are increasingly recognized as key to address the global food crisis and improve environmental sustainability, including reducing nitrous oxide (N₂O) emissions. However, the specific effects on N₂O emissions of different crops in these rotations and the underlying incidence on microbial processes remain underexplored. In a six-year field study, we compared N₂O emissions from traditional wheat-maize rotation with diverse rotations, including legumes (peanut, soybean), ryegrass, sorghum, and sweet potato. We also examined the microbial functions associated with nitrogen cycling based on functional annotation of prokaryotic taxa (FAPROTAX) analysis. Our study showed that diversified crop rotations with reduced synthetic fertilization and irrigation can reduce N₂O emissions by 23 %-49 % compared to conventional rotations. These reductions were supported by increases in soil organic carbon, soil carbon/nitrogen ratio and decreases in the relative abundance of denitrifying microorganisms, particularly observed in rotations with soybean and sweet potato. However, the spring maize and peanut-based rotation had higher emission factors than traditional wheat-maize rotation due to lower initial crop nitrogen uptake and lower nitrogen use efficiency, respectively. Changes in the microbial community structures of nitrification and denitrification processes, including increased activity of ammonia-oxidizing bacteria MND1 and archaea Candidatus Nitrososphaera in legume and sweet potato rotations, and a shift in denitrifying microbes of diverse rotations (a decrease in Rhodoplanes and an increase in Paracoccus), significantly contributed to the overall reductions in emissions in all other investigated rotation systems. Understanding the microbial mechanisms that control N₂O emissions from agricultural soils will enable the development of more effective and crop-specific strategies to further reduce greenhouse gas emissions.