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Grantee Research Project Results

Grantee Research Project Results

Novel Molecular Methods for Probing Ancient Climate Impacts on Plant Communities and Ecosystem Functioning: Implications for the Future

EPA Grant Number: FP917179
Title: Novel Molecular Methods for Probing Ancient Climate Impacts on Plant Communities and Ecosystem Functioning: Implications for the Future
Investigators: Bush, Rosemary Tolbert
Institution: Northwestern University
EPA Project Officer: Just, Theodore J.
Project Period: September 21, 2010 through September 20, 2013
Project Amount: $111,000
RFA: STAR Graduate Fellowships (2010)
Research Category: Academic Fellowships , Fellowship - Global Change

Description:

Objective:

The goal of my research is to elucidate the functional dynamics of plant communities and ecosystems in response to climate change in the geologic past. To accomplish this, I intend to investigate how preserved biomolecules in plant fossils and sediments can distinguish between angiosperms, gymnosperms, and deciduous and evergreen plants. I also intend to investigate the seasonal dynamics of leaf nitrogen use in deciduous and evergreen plants in order to probe differences in nitrogen allocation between the two groups.

Synopsis
Analysis of ecosystem responses to global warming in the geologic past will help us predict the ecological effects of modern climate change. My research compares plant groups (e.g. evergreen and deciduous) using 1) biomarkers (alkanes) in modern and fossil plants to track past changes in plant communities and 2) carbon isotopes in leaf amino acids to study nitrogen use. The combined molecular tools aid interpretation of the climate change impact on plants, ecosystems, and nutrient cycles.

Approach:

Using leaves collected across a growing season from modern plants, I will analyze the stable carbon isotope ratios of carboxyl carbons in leaf amino acids in order to investigate potential differences in biosynthetic discrimination and nitrogen allocation between deciduous and evergreen species. Additionally, my research involves carbon isotope analysis of leaf wax hydrocarbons (alkanes) in order to investigate a second biomolecular distinction between deciduous and evergreen species, one which can be preserved in ancient soils and sediments and serve as a proxy for plant community composition changes during past climate change. First, the molecular composition of modern plants must be characterized for interpreting the fossil molecular record. I will then test fossils from the Late Cretaceous and the Paleocene-Eocene boundary, both of which are periods of Earth’s history marked by warm global climates. Thus, I will apply novel studies of modern plants to follow changes in the biomolecular signals of plant groups through past greenhouse climate conditions.

Expected Results:

In examining amino acids, I anticipate an isotopic distinction between deciduous and evergreen plant species that is not confounded by the taxonomy of angiosperms and gymnosperms. The variance in carbon isotope ratios is caused by shifting biosynthetic pathways and metabolic carbon sources in the leaves, and is related to nitrogen use because the vast majority of plant nitrogen is found in protein amino acids. I expect also to confirm a molecular and isotopic distinction between similar groups (deciduous and evergreen, angiosperm and gymnosperm) through analysis of leaf wax alkanes in modern plants. I anticipate that by constraining the controls, whether taxonomic or functional, on carbon isotope fractionation in leaf wax alkanes, we can greatly clarify the interpretation of alkanes as ancient plant and ecosystem biomarkers. In this way, we can track changes in the composition of ancient ecosystems during warm periods in Earth’s history.

Potential to Further Environmental/Human Health Protection
Plant biomolecules serve as both the mediators of a plant’s response to its environment and as records of past plant-environment interactions, and once the biochemical relationships between plant physiology and modern environment are characterized, we can use those relationships to analyze fossilized plant biomarkers from ancient ecosystems. Using biomarker-based knowledge of plant community dynamics under past warm climate regimes, we can predict the responses of modern plant communities to a future warming climate. In this way, we can use molecular tools to further our understanding of ancient ecosystems in order to better predict ecosystem changes under a no-analogue future climate state.

Supplemental Keywords:

climate change, terrestrial ecology, paleoecology, plant functional types, carbon isotope ratios, n-alkanes, amino acids, PETM, Cretaceous,

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The perspectives, information and conclusions conveyed in research project abstracts, progress reports, final reports, journal abstracts and journal publications convey the viewpoints of the principal investigator and may not represent the views and policies of ORD and EPA. Conclusions drawn by the principal investigators have not been reviewed by the Agency.

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