Methane rhizospheric oxidation and its ecosystem significance across different aquatic plant species

Abstract Vegetated inland water habitats are important global emitters of methane (CH 4 ), but the variability in their CH 4 emission is poorly understood, making estimates and predictions uncertain. Methane is believed to be primarily released into the atmosphere via plant lacunal tissues in dense vegetated zones, although experiments have also shown that a large fraction of CH 4 can be consumed in the rhizosphere before it diffuses into the roots. Methane rhizospheric oxidation measurements have been limited to few species in situ, and it is still unclear how it differs between species. To determine the implications of CH 4 rhizospheric oxidation for plant-CH 4 release, I measured CH 4 rhizospheric oxidation and transport rates for 11 plant species with different gas transport efficiencies using dual isotopes in situ. Overall, the fraction of CH 4 produced that was oxidized was higher for plants that transport gases efficiently (up to 81%), and was negatively correlated to plant CH 4 release. These findings suggest that CH 4 oxidation decreases CH 4 release from plants that efficiently transport gases, although further studies are needed to assess the causality of this relationship. Such mechanistic understanding of plant-CH 4 release is necessary to define aquatic plant functional types with contrasting CH 4 emissions, and to reduce uncertainties in estimates of CH 4 freshwater emissions.