Aboveground living plant-based methane production does not dominate methane emissions in terrestrial ecosystems

This review highlights aboveground living plant-based methane production and evaluates its quantities in terrestrial ecosystems globally. The estimated quantities collectively explain only ~ 2% of aboveground living plant-based methane emissions. Aboveground living plant-based methane (CH₄) processes and fluxes have gained increasing attention over the last decades. However, aboveground living plant-based CH₄ production and its quantities in terrestrial ecosystems are not well known. For profoundly understanding the CH₄ processes and fluxes, we need to clarify aboveground living plant-based CH₄ production and evaluate its quantities in terrestrial ecosystems. The vertical pattern (from rhizosphere to canopy of plants, and vice versa) of the CH₄ production shows prominent variability across the various types of vegetated ecosystems, with especially large uncertainties in forests, and may moderately influence the vertical patterns of living plant-based CH₄ oxidation and emissions. Aboveground living plant-based CH₄ can be produced by microbial and non-microbial mechanisms. Microbial CH₄ is primarily produced in wet vegetation niche, while non-microbial CH₄ is typically produced in plant foliage under environmental stressors. The global aboveground living plant-based CH₄ production is summarized at the quantities of about 2.26 (1.11-3.87) Tg CH₄ yr^-1, and their uncertainties and complexities are further discussed. We suggest that aboveground living plant-based CH₄ production and its relationships with aboveground living plant-based CH₄ transport and emissions require more research, particularly within forest ecosystems.