PNNL

Abstract

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 dynamics in wetland ecosystems. Based on a literature review, we propose four main CH4-relevant root function categories in our framework: gas transport, carbon (C) substrate provision, physicochemical influences and root system architecture. We discuss how individual root traits influence CH4 production, consumption, and transport (PCT) within and between these categories. Our findings reveal knowledge gaps concerning trait functions in physicochemical influences, and the role of mycorrhizae and temporal root dynamics in PCT. We emphasize the need to integrate root traits from different categories, size and functional classes and along environmental gradients, and to follow standardized measurement protocols and vocabularies developed in root ecology. Our conceptual framework identifies relevant belowground plant traits that will help accurately predict wetland CH4 dynamics under global change.