METHANOGENESIS AND NITROGEN FIXATION: UNDERSTANDING THEIR INTERCONNECTION IN FRESHWATER WETLANDS

Wetlands, the largest source of natural methane, play a significant role in the carbon cycle. A pathway interconnecting wetlands’ carbon and nitrogen cycles is potentially evident as some methanogens harbor nifH, a key gene for nitrogen (N) fixation. To date, the duality of methanogens in performing both processes has largely been underexplored. This study aims to fill knowledge gaps on the strength of this coupling across environmental gradients. We investigated the correlation between methanogenesis and nitrogen fixation rates in freshwater wetlands and used N-15 DNA-stable isotope probing (SIP) to detect nitrogen-fixing microbial communities. Four wetland sites were selected based on unique geochemical characteristics of high iron, sulfate, organic carbon, and low phosphorus levels. The wetland sediments were incubated under atmospheric nitrogen in the dark at 25℃ with the addition of substrates: hydrogen and carbon dioxide (4:1), acetate, trimethylamine, and nothing (control). Over 14 days, methane production and nitrogenase enzyme activity were measured. A significant positive relationship was observed between the methane and nitrogen fixation rate constants normalized to the controls at only the organic carbon-rich wetland (p=0.05, rho=0.68, n=9). Ongoing is the sequencing of N-15 labeled DNA to identify the active N-fixing methanogens. Our study may inform future management actions in response to climate change as we will better understand the interconnectivity of methane emissions and nitrogen cycles in freshwater wetlands.

Presentation Preference: Oral

Primary Presenter: Lien Tran, Natural Resources Research Institute; University of Minnesota Duluth (Lien21Tran@gmail.com)

Authors:

Lien Tran, Natural Resources Research Institute; University of Minnesota Duluth  (Lien21Tran@gmail.com)

Chan Lan Chun, Natural Resources Research Institute; University of Minnesota Duluth, Civil Engineering Department; University of Minnesota Duluth  (chun0157@d.umn.edu)

Satoshi Ishii, Department of Soil, Water, and Climate; University of Minnesota, BioTechnology Institute; University of Minnesota  (ishi0040@umn.edu)