Plant Root Carbon Inputs Drive Methane Production in Tropical Peatlands

Tropical peatlands are carbon-dense ecosystems that are significant sources of atmospheric methane (CH). Recent work has demonstrated the importance of trees as an emission pathway for CH from the peat to the atmosphere. However, there remain questions over the processes of CH production in these systems and how they relate to substrate supply. Principally, these questions relate to the relative contribution of recent photosynthetically fixed carbon, released as root exudates, versus carbon substrate supply from the slowly decomposing peat matrix to CH emissions within these ecosystems. Here, we examined the role of root inputs in regulating CH production inferred from soil emissions using a combination of in situ tree girdling, in situC natural abundance labelling via stem injections, and a CO labelling of transplanted plants of two contrasting plant functional types, a broadleaved evergreen tree, and a canopy palm. Girdling of broadleaved evergreen trees reduced CH fluxes by up to 67%. Stem injections of trees and palms with a natural abundance label resulted in significant isotopic enrichment of CH fluxes, reinforcing the link between root carbon inputs and peat CH fluxes. Ex situCO labelling of plants resulted in significant C enrichment of peat CH fluxes. Taken together, our results demonstrate for the first time that plant root exudates make a substantial contribution to CH production in tropical peatlands.