The power of “Green” Energy: plant trait influences on microbial competition and greenhouse gas production

Abstract

Abstract Background/Questions/Methods Species vary in the eco-physiological traits they possess which means species may differentially influence ecosystem functions such as microbial activity. In wetland ecosystems it is important to understand how different plant species influence microbial competition for resources because competition affects microbial respiration and one of the products of anaerobic microbial respiration is methane, a potent greenhouse gas. Plants influence the availability of substrates for microbial respiration, both available carbon and terminal electron acceptors (such as Fe(III)). Because methanogenic microbes must compete with other microbes for respiration substrates and can be out-competed if conditions are more favorable for other microbes, plants can influence the outcome of microbial competition as well as overall rates of microbial activity by changing substrate availability. In this study, we examined how plant traits related to plant productivity and carbon inputs (belowground and total biomass, and photosynthesis) and plant traits related to oxygen inputs and terminal electron acceptor availability (root porosity and Fe(III) on roots) influence microbial competition and methane production from wetland soils. Results/Conclusions Overall microbial respiration rates were positively correlated with plant productivity, but methane production was negatively correlated with plant productivity, suggesting that carbon inputs were not stimulating methanogenesis. Evidence that alternative microbial respiratory pathways were stimulated with higher plant productivity included: (1) higher CO2:CH4 ratios from the microbial communities of plants with higher productivity and (2) greater oxidized iron (Fe(III)) on roots of plants with higher productivity. Both of these results indicate that as plant productivity and belowground biomass increased, microbes used alternative respiration pathways and produced less methane. These results indicate that plant community composition plays an important role in methane production in wetlands. Therefore, human disturbances, such as climate change, invasive species, and eutrophication, which result in shifts in plant community composition are likely to have profound effects on methane production in wetlands.