The hidden roots of wetland methane emissions

Wetlands are the largest natural source of methane (CH₄ ) globally. Climate and land use change are expected to alter CH₄ emissions but current and future wetland CH₄ budgets remain uncertain. One important predictor of wetland CH₄ flux, plants, play an important role in providing substrates for CH₄ -producing microbes, increasing CH₄ consumption by oxygenating the rhizosphere, and transporting CH₄ from soils to the atmosphere. Yet, there remain various mechanistic knowledge gaps regarding the extent to which plant root systems and their traits influence wetland CH₄ emissions. Here, we present a novel conceptual framework of the relationships between a range of root traits and CH₄ processes in wetlands. Based on a literature review, we propose four main CH₄ -relevant categories of root function: gas transport, carbon substrate provision, physicochemical influences and root system architecture. Within these categories, we discuss how individual root traits influence CH₄ production, consumption, and transport (PCT). Our findings reveal knowledge gaps concerning trait functions in physicochemical influences, and the role of mycorrhizae and temporal root dynamics in PCT. We also identify priority research needs such as integrating trait measurements from different root function categories, measuring root-CH₄ linkages along environmental gradients, and following standardized root ecology protocols and vocabularies. Thus, our conceptual framework identifies relevant belowground plant traits that will help improve wetland CH₄ predictions and reduce uncertainties in current and future wetland CH₄ budgets.