Sunlight exposure replaces the function of microbial enzymes needed to degrade DOM
EMSL Project ID
50950
Abstract
About half of the dissolved organic matter (DOM) released from land is converted to CO2 in inland waters (e.g., streams, rivers, lakes), driving a CO2 flux to the atmosphere roughly equal to the net amount of CO2 removed from the atmosphere by land or ocean plants each year (~ 2 Pg C y-1). DOM is converted to CO2 by microbial respiration, and a key control on microbial respiration of DOM is prior sunlight exposure (photo-oxidation of DOM). Microbial and photo-oxidation of DOM to CO2 take place concurrently in sunlit surface waters, but little is known about how sunlight and microbes interact to carry out this conversion. For this reason, conceptual models fail to explain why photo-oxidation of DOM sometimes increases and sometimes decreases microbial respiration, or why rates of respiration vary with the species composition of microbial communities. Determining the controls on coupled "photo-bio" conversion of DOM to CO2 is essential for understanding the drivers of CO2 fluxes to the atmosphere from soils or inland waters in any biome, but may be particularly important in the warming Arctic where thawing permafrost soils will export more terrestrial DOM from land to water. Recent advances in high-resolution analysis of microbial genomics and DOM chemistry make it possible to test the idea that rates of microbial processing increase when sunlight exposure of DOM produces compounds that microbes are genetically equipped to degrade without expensive enzymes. Alternatively, when sunlight removes compounds microbial communities were already degrading, then microbes must adapt over time to metabolize new substrates and their activity decreases. This project will answer two questions: (Q1) Does sunlight replace the function of enzymes to degrade aromatics and to decarboxylate and oxidize DOM?
(Q2) How does longer-term adaptation of microbial communities affect the rate of DOM degradation?
These questions will be answered with experimental incubations of microbial communities with DOM leached from surface organic mat soils and deeper permafrost soils from two dominant arctic landscapes (upland, lowland). DOM leached from both landscapes and soil depths will be exposed to sunlight, sterile filtered, and fed to native microbial communities where microbial abundance, respiration, production, and genomics will be measured during the incubations. Microbial pathways of DOM conversion to CO2 will be identified by measuring microbial gene abundance (metagenomics) and the expression of those genes (metatranscriptomics), and molecular functional groups and formulas of DOM that are consumed and produced during incubations will be identified by solid-state 13C-NMR and stable-isotope probes by FT-ICR mass spectrometry, respectively. Preliminary results were generated at EMSL and JGI, and the capabilities of EMSL and JGI are required to conduct this research.
Project Details
Project type
FICUS Research
Start Date
2019-10-01
End Date
2022-09-30
Status
Closed
Released Data Link
Team
Principal Investigator
Co-Investigator(s)
Team Members