Abstract
Tropical peatlands are a globally important source of methane, a potent greenhouse gas. Vegetation is critical in regulating fluxes, providing a conduit for emissions and regular carbon inputs. However, plant roots also release oxygen, which might mitigate methane efflux through oxidation prior to emission from the peat surface. Here we show, using in situ mesocosms, that root exclusion can reduce methane fluxes by a maximum of 92% depending on species, likely driven by the significant decrease in root inputs of oxygen and changes in the balance of methane transport pathways. Methanotroph abundance decreased with reduced oxygen input, demonstrating a likely mechanism for the observed response. These first methane oxidation estimates for a tropical peatland demonstrate that although plants provide an important pathway for methane loss, this can be balanced by the influence of root oxygen inputs that mitigate peat surface methane emissions.
Highlights
Tropical peatlands are an important part of the global carbon cycle, containing 104.7 Gt C, and constituting a significant source of methane (CH4) and carbon dioxide (CO2) emissions [1, 2]
This demonstrates the critical role of roots as regulators of tropical peatland greenhouse gas (GHG) fluxes through species-specific inputs of oxygen, which regulates microbial community abundance and the degree to which CH4 is consumed in the peat profile
Root exclusion resulted in a 92% reduction of CH4 fluxes, most likely driven by the 0.2%–3.3% reduction in root inputs of oxygen between root-accessible and closed mesocosms, and through changes in the balance of ebullition, plant-mediated and diffusion pathways
Summary
Tropical peatlands are an important part of the global carbon cycle, containing 104.7 Gt C, and constituting a significant source of methane (CH4) and carbon dioxide (CO2) emissions [1, 2]. Roots are well-adapted to waterlogged, anoxic conditions with aerial roots, pneumatophores and aerenchymateous tissue These adaptations represent a substantial pathway for GHG transport, with root aerenchyma mediating up to half of net CH4 emissions in the Amazon floodplain [10]. Roots can be a significant source of oxygen in otherwise anoxic conditions, due to diffusion from root tissue into the peat. These localised oxic conditions can suppress CH4 fluxes by inhibiting methanogenesis and/or driving methanotrophy [11]. The importance of this process in regulating peat surface GHG fluxes in tropical peatlands represents a critical knowledge gap, with evidence from temperate and boreal peatlands, as well as wetland ecosystems more widely, indicating substantial potential for oxygen to limit net CH4 fluxes [12, 13]. The relative importance of this process may differ in tropical peatlands versus northern climes, due to differences in vegetation type (generally tree and palm dominated versus moss dominated), higher temperatures and associated changes in rates of productivity and decomposition of organic matter [4]
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