Plant community effects on CH4 fluxes, root surface area, and carbon storage in experimental wetlands

Wetland creation is a form of ecological engineering that often relies on establishing a plant community to increase ecosystem services. However, we still lack understanding about how species composition and diversity affect certain wetland ecosystem functions associated with these ecosystem services. Our objective was to investigate the link between plant community (diversity and composition) and plant carbon storage, root surface area and methane (CH4) emission. We hypothesized that more diverse mixtures would 1) store more carbon in above and belowground biomass and 2) emit less CH4 due to increased root surface area and aeration. Three plant groups that represented different growth forms (i.e., “functional groups”: ferns, reeds and tussocks) were planted in mesocosms to represent four levels of functional diversity and every combination of functional groups at each diversity level. Unplanted mesocosms served as the zero diversity treatment. At peak biomass in 2014 and 2015, we harvested aboveground biomass and took soil cores from each mesocosm at 0-10 cm to determine the root biomass and surface area. Methane fluxes were measured in situ using a closed chamber system and a Picarro G2301 CRDS analyzer. Fluxes did not vary by functional group richness level or composition. Presence of the reed and tussock functional groups decreased fluxes; however, root surface area was not correlated with CH4 emission. Plant carbon storage was greater in all treatments containing tussocks (expect for the reed tussock mixture) compared with ferns grown alone. Functional group richness did not have a significant effect on plant carbon storage, however there was a positive trend. Root surface area increased 87% from the first to second year; however, there were no differences among functional group richness levels or mixtures. Our results indicate that planting reed and tussock functional groups in dense clumps during restoration could maintain a high level of carbon storage and relatively low CH4 emissions.