| |
| author |
Mason Scher
| | title |
Carbon Isotope Discrimination in Ginkgo: Testing A Paleo-CO2 Proxy
| | abstract |
Anthropogenic climate change poses a major threat to our current way of life.
Without understanding how earth systems will react to growing anthropogenic CO2
emissions, it is impossible to properly plan. Reconstructions of CO2 levels (paleo-CO2)
and other important environmental parameters from the geologic past give a long-term
record of earth system changes which are invaluable for understanding just how sensitive
earth systems are. While there are several methods of reconstructing paleo-CO2, more are
needed to corroborate existing reconstructions and to fill in important gaps in time. The
Paleocene-Eocene Thermal Maximum (PETM) was a transient warm peak about 56
million years ago and is the best analog of future climate change. Paleo-CO2
reconstructions are lacking during this important event, preventing an understanding of
how much atmospheric CO2 gave rise to the 5-8°C temperature increase of the PETM.
Ginkgo has been used widely to reconstruct CO2 levels in the geological past because
living Ginkgo biloba closely resembles common Mesozoic and Paleogene fossils of the
genus. Many Ginkgo fossils from around the time of the PETM have been collected, and
would be useful for paleo-CO2 reconstructions. Atmospheric CO2 levels in the geological
past have been inferred from the δ13C of plant fossils following experimental evidence in
Arabidopsis and Raphanus, where leaf-level discrimination against 13C (Δ13C, or
difference between δ13C of atmosphere and leaf) was found to increase with
pCO2. Higher pCO2 leads to higher CO2 within the leaf (Ci), allowing RuBisCO to more
strongly discriminate against 13C. Ginkgo has been used widely to reconstruct CO2 levels
in the geological past because living Ginkgo biloba closely resembles common Mesozoic
and Paleogene fossils of the genus. We therefore constructed an experiment to test if
Δ13C in Ginkgo was positively correlated with pCO2. For four years (2016-2019) we
grew Ginkgo biloba trees outdoors in open-topped chambers under ambient light and
temperature fluctuations but with CO2 levels of ~400, ~600, ~800, and ~1000 ppm (three
trees at each CO2 level). Data from the 2018 and 2019 growing season gave an
unexpected relationship between pCO2 and Δ13C where Δ13C has a slightly negative
relationship with pCO2. Our work shows that the relationship between Δ13C and pCO2 is
not the same in Ginkgo as in Arabidopsis and Raphanus. A compilation of studies of
Δ13C in a variety of species shows no consistent relationship to be used as a paleo-CO2
proxy. If the relationship of Δ13C to pCO2 varies among taxa, caution should be taken in
reconstructing ancient CO2 concentrations from Δ13C of mixed fossil organic matter or
molecular fossils. Further work with physiological data from this experiment may show
that stomatal regulation prevents Ci from increasing with increasing pCO2, which would
prevent Δ13C from increasing with increasing pCO2.
| | school |
The College of Liberal Arts, Drew University
| | degree |
B.A. (2020)
|
| advisor |
Dr. Ryan Hinrichs
|
| full text | MScher.pdf |
| |
