Assessing root-soil interactions in wetland plants: root exudation and radial oxygen loss

Abstract. Plant rhizosphere processes, such as root exudation and root oxygen loss (ROL), could have significant impacts on the dynamics and magnitude of wetland methane fluxes, but are rarely measured directly. Here, we measure root exudation and ROL from Schoenoplectus americanus and Spartina patens, two plants that have had opposite relationships between biomass and methane flux in field experiments. We found contrasting rates of ROL in the two species, with S. americanus releasing orders of magnitude more oxygen (O₂) to the soil than S. patens. At the same time, S. patens exudes high amounts of carbon to the soil, with much of that carbon pool reduced compared to exudates from other wetland species. This work suggests that the relative inputs of O₂ and carbon to the rhizosphere vary significantly between wetland plant species, potentially with major consequences on methane emissions, and highlights the importance of understanding how plant rhizosphere processes mediate soil biogeochemistry at a community level. As global change drivers continue to impact wetlands, future research should consider how feedbacks from plant rhizosphere processes may exacerbate or mitigate coastal wetland methane emissions.