The importance of plants for methane emission at the ecosystem scale

Methane (CH₄), one of the key long-lived atmospheric greenhouse gases, is primarily produced from organic matter. Accordingly, net primary production of organic matter sets the boundaries for CH₄ emissions. Plants, being dominant primary producers, are thereby indirectly sustaining most global CH₄ emissions, albeit with delays in time and with spatial offsets between plant primary production and subsequent CH₄ emission. In addition, plant communities can enhance or hamper ecosystem production, oxidation, and transport of CH₄ in multiple ways, e.g., by shaping carbon, nutrient, and redox gradients, and by representing a physical link between zones with extensive CH₄ production in anoxic sediments or soils and the atmosphere. This review focuses on how plants and other primary producers influence CH₄ emissions with the consequences at ecosystem scales. We outline mechanisms of interactions and discuss flux regulation, quantification, and knowledge gaps across multiple ecosystem examples. Some recently proposed plant-related ecosystem CH₄ fluxes are difficult to reconcile with the global atmospheric CH₄ budget and the enigmas related to these fluxes are highlighted. Overall, ecosystem CH₄ emissions are strongly linked to primary producer communities, directly or indirectly, and properly quantifying magnitudes and regulation of these links are key to predicting future CH₄ emissions in a rapidly changing world.