Microorganisms that consume methane can play an important role in controlling global climate since each molecule of methane is about 26 times more effective than carbon dioxide in the greenhouse effect. Although many studies have investigated soil methane consumption, they have focused on methane consumption in the presence of oxygen, overlooking the potentially important role of anaerobic methane consumption (anaerobic oxidation of methane; AOM). Humid tropical forests are globally significant sources of atmospheric methane, accounting for more than 17% of all methane emissions. Boreal and arctic wet soils also release significant quantities of methane to the atmosphere, producing over 10% of all methane emissions. It is important to identify and characterize processes and organisms that help to control methane fluxes from these biomes. Anaerobic oxidation of methane is a potentially important process not previously identified in tropical or boreal terrestrial systems. Preliminary work demonstrates that AOM does occur in both tropical and boreal soils. This dissertation project investigates AOM in soils from Luquillo Experimental Forest (Puerto Rico) and Bonanza Creek LTER (Alaska) as tropical and boreal model ecosystems. Microogranisms and their methane oxidizing activities will be analyzed using molecular and genomic techniques in combination with geochemical analyses.
The proposed research will advance our understanding of the microbial basis and distribution of anaerobic methane oxidation, and determine whether this soil process important in climate forcing. This knowledge will help us understand the possible impacts of land use change on the consumption of methane by soils. To help introduce young scientists to ecological research, undergraduate students will be involved in the project through the SPUR (Sponsored Projects for Undergraduate Research) program sponsored by the College of Natural Resources at UC Berkeley. Upon completion of this project, results will be published in peer-reviewed international journals and presented at international scientific conferences.
Microorganisms that consume methane play an important role in controlling climate change, since methane is approximately 26 times more effective than carbon dioxide in retaining heat in the atmosphere. Although many studies have investigated soil methane consumption, they have focused on aerobic methane consumption, overlooking the potentially important role of anaerobic methane consumption (anaerobic oxidation of methane; AOM). AOM is a considerable sink for the greenhouse gas methane in marine systems, but the importance of this process in terrestrial systems is less clear. Lowland boreal soils and wet tropical soils are two of the most dynamic terrestrial systems with regard to atmospheric methane cycles, yet little work has directly investigated AOM in these systems. We assessed the occurrence and potential importance of AOM in soils from Long Term Ecological Research sites in Alaska and Puerto Rico. We found that boreal peat soil and tropical mineral soil had the ability to consume significant quantities of methane under anaerobic conditions, and this process was biologically mediated. In both tropical and boreal soils, AOM was only observed when methane production was also occurring, and there is a strong correlation between rates of the two processes indicating that the oxidation of methane under anoxic conditions is related to methane production activity and not to nitrate, ferric iron, or sulfate reduction. Although anaerobic oxidation rates were much slower than aerobic methane oxidation rates in both tested soil systems, it is important to recognize that this process could play a measurable role in controlling net methane flux. This experiment provides an important first glimpse into the capacity for methane to be oxidized under anoxic conditions in wet tropical soil and boreal peat soil. Clearly, the total amount of methane oxidized by this process will be a function of land area, but the importance of AOM in reducing net methane flux from these soils will be dependent on environmental factors that affect the proportion of methane oxidized relative to methane produced. Results from this project advance our current understanding of whether anaerobic oxidation of methane mitigates climate forcing through methane consumption. This knowledge is fundamental to understanding the fate of atmospherically-reactive methane and the future impacts of land use change on the consumption of methane by soils. Much is still unknown about AOM in these soils and the need for additional investigation is compelling. Results from this project have been presented at international conferences and published in a peer-reviewed journal.
