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.

Birmingham Institute of Forest Research School of Geography Earth and Environmental Sciences University of Birmingham Birmingham UK

Department of Ecosystem Trace Gas Exchange Global Change Research Institute of the Czech Academy of Sciences Belidla 4a 60300 Brno Czech Republic

Faculty of Science and Engineering Southern Cross University Lismore NSW Australia

Institute of Botany Chinese Academy of Sciences Nanxincun 20 Xiangshan Beijing 100093 China

Institute of Environment and Sustainable Development in Agriculture Chinese Academy of Agricultural Sciences Beijing 100081 China

School of Life Sciences Qufu Normal University 57 Jingxuan West Road Qufu 273165 China

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