60th Annual Report on Research 2015

Overview. Lignite is important for electricity generation and may be used as a substrate for Fisher-Tropsch synthesis of liquid fuel. Its precursor is lignin the second most important plant biochemical, involved in structural support. Recently lignin in living trees has been shown to encode the D/H of precipitation, providing for the potential to record hydrological changes if those primary signals are preserved. The aims of this PRF funded project are to take the PIs research in new directions to understand the fundamental D/H systematics in living wood, sedimentary lignin in peats and on into lignites. Fundamental scientific research questions include the magnitude of fractionations associated with biosynthesis, variability between plant species, diagenetic alteration and catagenic alteration. The ultimate motivation pertaining to PRF relevance is to assess the diagnostic potential of D/H of methoxyl groups within lignites

Work done. In work supported by this PRF award, we (the postdoc and PI) have analyzed the D/H ratios of methoxyl on pristine lignin in laboratory standards, living wood samples, sedimentary lignin in the form of peats and lignites of varying maturities. While the preparative and analytical chemistry follows recently established methods for methoxyl D/H ratios in tree wood, we have extended the range of sample types and applications and have developed methods suitable for analysis of the target analyte D/H of methoxyl groups in sediments from peats to lignites. The application to these substrates represents a new direction for the proxy and the principal investigator’s laboratory. We have developed new contacts with researchers specializing in tropical forests, tropical peats and coal geology in order to select the best test case environments and samples with which to test this new approach. We (the postdoc and PI) have presented posters at the Organic Geochemistry Gordon Research Conference in summer 2014.

Scientific outcomes. Our analytical results to date resolve the extent to which D/H ratios in lignin record the D/H ratios of precipitation and to what extent they are modulated by large biosynthetic fractionations, and then subsequently modified during burial and diagenesis.

Part 1. The PI has characterized the D/H ratios of methoxyl in tropical trees across a megadiverse ecological gradient from the tropical Amazon to the high Andes. I analyzed the D/H of plant stem waters and the D/H of stream waters and the D/H of lignin methoxyl in stem wood from tropical trees. Interspecies variability dominated over the environmental gradient in precipitation isotopes. I am now testing whether the gradient in precipitation isotopes is being overridden by an opposing gradient in the use of stored carbohydrates in year 2.

Part 2. Postdoc Ponton has characterized the D/H ratios of sediments forming from plants in a range of tropical peats that vary in minerotrophic status and ecology in tropical Peru. These peats are selected as analogues for lignites from low latitudes and warm periods of Earth History. He found isotopic variability between sites with different vegetation covers. He also generated a downcore record spanning 9ka from an 8m core, which might reflect a shift from open water palm swamp to closed palm swamp. Additional tests will be conducted in year 2 and the PI has been mentoring the postdoc on writing up the results for publication.

Part 3. Postdoc Ponton made the first measurements of D/H of methoxyl from lignites from a well-characterized deposit in Poland. He found an overall trend to more D-depleted values in more mature horizons. This is opposite to predictions for D-enrichment expected if the process of diagenesis involves kinetic effects during losses. However it is not known if the trend is related to the large variability between samples given the strong effects associated with vegetation type (also seen in part 1 and 2). Ponton then sought to extend the maturity gradient, however he found methoxyl yields were too low for detection in coals, as expected given the structural changes associated with catagenesis. The postdoc will lead author a manuscript for Organic Geochemistry.

Impact on career outcomes. Postdoctoral researcher Camilo Ponton was engaged in this PRF research for 14 months. He has acquired samples and data relating to the scientific objectives of this PRF proposal to study lignin from living trees through to lignin in peats and finally lignites in Miocene age deposits. During 2014 he successfully published a paper from his prior work in Geophysical Research Letters and he applied to sail on an expedition for 2 months to the Bengal Fan, which he did after appointment on the PRF project at USC. This included being mentored in writing a proposal that was funded to support his salary on board ship and research beyond. He is now a postdoctoral researcher at the California Institute of Technology and has proceeded there for a second postdoc, where he is learning further analytical techniques and continuing his professional development in compound specific isotopic work in the research group of John Eiler. Publications arising from his work on the PRF award are expected to be finalized in 2015.