Photosynthetic Adaptation to Carbon Dioxide Gradients in Yellowstone: A glimpse into the future of climate change?

In addition to its well-known thermal features, Yellowstone National Park (YNP) contains point sources of carbon dioxide that are elevated in magnitude above atmospheric CO2 by two orders (300 > 10,000 ppm). Spatial gradients in both CO2 and DIC concentration surrounding these features (fumaroles, seeps, springs) exist to which photosynthetic organisms could, potentially, undergo long-term adaptation that would take decades to recreate in controlled laboratory experiments. We used YNP as a natural laboratory to investigate photosynthetic adaptation to CO2 concentrations (300 -6000 ppm) during the course of two weeks of field experiments in 2019. We have measured photosynthetic rates as the light-induced electron transfer from water (O₂ evolution) to PSII terminal carrier (plastoquinone) and to PSI terminal carrier (NADP+), and the subsequent utilization of NADPH in the dark fixation reaction of CO2 assimilation. Measurements were done using Chl fluorescence using a portable Fast Repetition Rate Fluorometer. We will present preliminary results on the kinetics of four stages of electron transfer: water oxidation and charge separation in PSII, QA reduction and filling of the PQ pool, reduction of NADP+ and CO2 assimilation. Preliminary conclusions based on two higher plants illustrate that natural CO2 gradients significantly influence the flux of electrons through the light reaction(s) in response to CO2 availability such that CO2 assimilation rates are affected in turn. Upon completion of this project, these data will provide a resource to the community for more accurately forecasting how C3 photosynthesis (Calvin cycle) and biomass productivity of agricultural crops could most likely adapt to CO2 driven climate change.