NSF Postdoctoral Fellowship in Biology FY 2017: Reconstructing CO2 fertilization with herbaria

Anderegg Leander, Palo Alto CA

Investigators

Abstract

This is an NSF Postdoctoral Research Fellowship in Biology, under the program Research Using Biological Collections. The fellow, Leander Anderegg, is conducting research and receiving training that utilizes biological collections in innovative ways, and is being mentored by two sponsoring scientists at two host institutions: Todd Dawson (University of California-Berkeley) and Joseph Berry (Carnegie Institute for Science). The fellow is investigating how plants have responded to rising amounts of carbon dioxide (CO2) in the atmosphere over the past century, in order to predict how plants will respond to increasing human CO2 emissions in the future. Plants are like merchants: they essentially trade water to the atmosphere in exchange for the CO2 they need to produce sugars through photosynthesis. By burning fossil fuels, humans have changed the global carbon-water exchange rate in plants' favor by making it less water-expensive to 'buy' CO2 from the atmosphere. Theoretically, this could increase plant growth around the world, improving crop yields and increasing how much of our CO2 emissions ecosystems can absorb from the atmosphere in the future. However, recent observations suggest that this CO2 fertilization effect is far more limited and variable than previously thought. This research explores why CO2 fertilization responses are so complex, focusing on how drought stress and differences between plant species determine if and how a plant responds to rising atmospheric CO2. The fellow is using hundred-year-old plant samples from museum herbarium collections along with modern samples collected from the same locations to reconstruct how tree species across California have responded to rising CO2. The fellow is comparing the morphology, anatomy and chemical composition of these historical and modern leaves to determine how trees have changed their physiology over the past century. The historical and contemporary records of plant responses to CO2 collected through this research are also revealing how CO2 fertilization varies across species and climates. The fellow is using this information, along with tree growth reconstructions from tree cores and mechanistic photosynthesis models, to understand how water availability and species physiology dictate tree responses to elevated CO2. This work is helping to reconcile the results of short-term CO2 fertilization experiments and long-term observations from tree rings of the exchange rate between water and CO2. A nuanced understanding of the plant traits and environmental conditions that lead to different CO2 fertilization responses will improve our ability to predict terrestrial ecosystem function under accelerating environmental change. The fellow is being trained in plant anatomical, isotopic and modeling techniques while also developing new methods for unlocking critical information from underused herbarium collections.