Coupled biological and photochemical degradation of DOM in the Arctic
(NSF-DEB 1754835,1753731)
P.I.s: Byron C. Crump, Rose M. Cory, George W. Kling
Graduate Students: Natasha Christman, Karl Romanowicz, Emma Rieb
Polar-TREC Teachers: David Walker
Technicians: Jason Dobkowski, Catherine Polik, Emma Daily
Overview: The important role of inland waters in global C cycling and releasing CO2 to the atmosphere is well established, but the mechanisms by which terrestrial dissolved organic matter (DOM) is converted to CO2 remain poorly constrained. DOM degradation has been attributed mainly to bacterial activity in sediments and surface waters, but recent findings show that photochemistry plays a substantial, quantitative role in aquatic C cycling. DOM leached from soils can be very labile to photochemical alteration, which in turn can profoundly alter rates of DOM respiration, metabolic pathways expressed by microbial communities, and microbial community diversity. Thus, rates of DOM degradation are controlled by both microbial and photochemical processes, but the interaction between these two processes is poorly understood. For example, conceptual models fail to fully explain why photo-alteration of DOM can both amplify or reduce microbial processing of DOM, or why rates of DOM respiration vary with microbial community composition. These knowledge gaps will be addressed by integrating studies of photochemical and biological processing of DOM with a set of environmentally-relevant experiments and high-resolution chemical and genetic measurements aimed at (a) linking the diversity and genetic mechanisms of DOM-respiring microbial communities to the chemistry of the biologically-relevant portions of terrestrial DOM, and (b) quantifying the metabolic response of diverse microbial communities to the photochemical production or removal of DOM compounds.
Intellectual Merit : This proposed research will be carried out in the Arctic where thawing permafrost and the release of CO2 is predicted to amplify global warming. The research goal is to identify the biological and chemical mechanisms by which microbes and sunlight interact to degrade terrestrial DOM, and to answer three questions: (Q1) How are microbial metabolic pathways controlled by DOM chemistry? This question will be answered with experimental incubations of natural microbial communities with filter-sterilized DOM leached from soils (surface organic, permafrost mineral) from two dominant arctic landscapes. In order to quantify microbial enzymatic reactions used in DOM degradation, metagenomics and metatranscriptomics will be used to assess microbial gene abundance and expression patterns, and FTICR MS and optical characterization will be used to identify molecular formulas and fractions of DOM that are consumed and produced during incubation; (Q2) How does DOM exposure to sunlight alter the microbial metabolic pathways used to degrade DOM? This question will be answered by expanding the experiments used for Q1 by exposing leached soil DOM to sunlight; (Q3) What is the contribution of long-term adaptation of microbial communities to the rate of DOM degradation? This question will be answered by measuring microbial abundance, production, respiration, and community composition during the experimental incubations described above.
Broader Impacts: Because future generations will increasingly face the burden of climate change, engaging high school and college students in science is critical for a cross-cultural appeal to discover and apply solutions to climate change. To engage this next generation this proposal will (1) support two graduate students, (2) support Research Experience for Undergraduate fellows to participate in summer field sampling and experiments, (3) recruit undergraduates from the Oregon State University Honors College to participate in laboratory analysis and bioinformatics work, (4) continue PI participation in the NSF PolarTrec program through which they developed a K-12 teacher network to create lesson plans, and (5) partner with ongoing efforts at the University of Michigan, including EARTH Camp and M-STEM, programs that facilitate high school and incoming freshman to stick with science at critical junctions.
Publications
Bowen, J. C., Ward, C. P., Kling, G. W., Cory, R. M. 2020. Arctic amplification of global warming strengthened by sunlight oxidation of permafrost carbon to CO2. Geophysical Research Letters 47(12):e2020GL087085. doi.org/10.1029/2020GL087085
Nalven, S. G., Ward, C. P., Payet, J. P., Cory, R. M., Kling, G. W., Sharpton, T. J., Sullivan, C. M., and B. C. Crump. 2020. Experimental metatranscriptomics reveals the costs and benefits of dissolved organic matter photo‐alteration for freshwater microbes. Environmental Microbiology. doi: 10.1111/1462-2920.15121
Trusiak, A., L. A. Treibergs, G. W. Kling, and R. M. Cory. 2019. The controls of iron and oxygen on hydroxyl radical (•OH) production in soils. Soil Systems 3, 1, 1-23; doi:10.3390/soilsystems3010001
Cory, R. M. and G. W. Kling. 2018. Controls on DOM degradation along the aquatic continuum: the influence of interactions between light, chemistry, and biology. Limnology and Oceanography Letters doi: 10.1002/lol2.10060
Trusiak, A., L. A. Treibergs, G. W. Kling, and R. M. Cory. 2018. The role of iron and reactive oxygen species in the production of CO2 in arctic soil waters. Geochimica et Cosmochimica Acta 224: 80–95. doi.org/10.1016/j.gca.2017.12.022
Cory, R. M., and G. W. Kling. 2018. Interactions between sunlight and microorganisms influence dissolved organic matter degradation along the aquatic continuum. Limnology and Oceanography Letters 3: 102–116. doi:10.1002/lol2.10060
Ward, C. P., S. G. Nalven, B. C. Crump, G. W. Kling, and R. M. Cory. 2017. Photochemical alteration of organic carbon draining permafrost soils shifts microbial metabolic pathways and stimulates respiration.Nature Communications 8:8.
Ward, C. P., and R. M. Cory. 2016. Complete and Partial Photo-oxidation of Dissolved Organic Matter Draining Permafrost Soils. Environmental Science and Technology 50: 3545–3553. doi:10.1021/acs.est.5b05354
