Opportunities for methanotrophs to contribute to sustainable agronomy. A review

Abstract

Methanotrophs are methane (CH₄)-oxidizing proteobacteria and archaea that occupy most ecological niches. Their contributions towards regulating global CH₄ budgets, potential to generate high-value carbon products, and capacity to mitigate contaminant impacts have been exhaustively reviewed. Another, less explored, area where methanotrophs offer enormous potential is sustainable agronomy. Agricultural settings host extensive methanotrophic communities. However, disturbance within these landscapes can disrupt community function and impede methane oxidation efficiency. In this review, we evaluate the opportunity for abating agricultural CH₄ emissions via methanotrophy using a novel approach that integrates potential across multiple emission sources. First, we appraise agricultural settings which are simultaneously CH₄ emission and methanotrophy hotspots. We then estimate the quantity of CH₄ available for abatement in these hotspots and propose methods to enhance methanotrophy. Finally, we evaluate and synthesize ecosystem services that methanotrophs offer to the agronomic sector. We identified four substantial agricultural CH₄ hotspots with high potential for improved CH₄ oxidation: (1) rice farming, (2) livestock lagoons/ponds, (3) grazing pastures on heavy soils, and (4) tropical/lowland cane farming. The total pool of anthropogenic CH₄ that can be mitigated in these systems exceeds 1.5 Gt carbon dioxide equivalents (CO₂-e) year⁻¹, which is almost 20% of total global anthropogenic CH₄ emissions. Within these systems, methanotroph resilience and re-establishment can be enhanced by the following: using alternatives to acidifying ammonia-based fertilizers; aerating soils with high surface area amendments, like biochar; reduced tillage; promoting biological activity on the boundaries of livestock ponds; and soil application of biofertilizers containing plant growth–promoting rhizosphere microorganisms. The potential agricultural services offered by methanotrophs are profound and include increased nitrogen and carbon fixation, and soil nutrient mining. We conclude that enhancing methanotrophy in agricultural settings not only offers an opportunity to meaningfully reduce emissions driving climate change, but also presents attractive economic and environmental benefits for the agronomic sector.