Exploring Sulfate as an Alternative Electron Acceptor: A Potential Strategy to Mitigate N 2 O Emissions in Upland Arable Soils

Abstract

Agricultural activities are a significant source of nitrous oxide (N 2 O), accounting for approximately 60% of global emissions, highlighting the urgent need for innovative strategies to mitigate N 2 O emissions. Microbes conserve nearly as much energy with nitrate (NO 3 − ) as oxygen (O 2 ) respiration under limited O 2 availability. Thus, microorganisms prioritize NO 3 − , limiting exploration of alternative electron acceptors (EAs) to inhibit N 2 O emissions through NO 3 − respiration in upland arable soils. Current approaches remain insufficient, and the interactions between alternative EA reduction and pathways for N 2 O emissions remain poorly understood. This study evaluated oxidized iron, manganese, and sulfate as alternative EAs to reduce N 2 O emissions, along with the effects of zero‐valent metals (ZVMs). Metal sulfates (MSs) significantly minimized N 2 O emissions by inhibiting denitrification rather than altering nitrification in microcosms, as supported by isotope mapping and inorganic nitrogen concentrations. Among others, putative complete denitrifiers, N 2 O reducers, and sulfate reducers were stimulated, whereas ZVMs stimulated N 2 O emissions and 16S rRNA gene abundance. Moreover, the abundance of denitrifier‐related genes ( nirK , nirS , norB , and nosZ ) consistently decreased under MS treatments, while dsrA mRNA abundance significantly increased. Sulfate (SO 4 2− ) addition reshaped the soil microbial community by enriching sulfur‐cycling taxa—including sulfate‐reducing and sulfur‐oxidizing bacteria—while suppressing nitrifiers such as Nitrospira , potentially disrupting nitrification–denitrification coupling. Ureibacillus thermosphaerius , harboring genes for denitrification and SO 4 2− reduction, increased under MS treatment. These shifts likely redirected electron flow toward SO 4 2− respiration, reducing NO 3 − utilization and contributing to N 2 O mitigation. Field‐based manipulation experiments over 2 years demonstrated the feasibility of MSs in upland arable soils, reducing yield‐scaled N 2 O emissions by 21.5% without compromising crop yields. A systematic literature review and meta‐analysis revealed that SO 4 2− application mitigated N 2 O emissions by an average of 9%, with over 70% of observations showing a decreasing trend, underscoring its potential as an effective soil amendment for sustainable agriculture.

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