A central goal of biological oceanography has been to determine the rates of primary production in the ocean. With the advent of satellite technology, scientists are now able to estimate algal chlorophyll biomass on appropriate time and distance scales, but the estimation of production from chlorophyll requires an understanding and application of the physiological mechanisms by which we can relate chlorophyll abundance to a carbon production rate. The photosynthesis vs. irradiance (PE) relationship has long proven a useful construct for describing variability in algal production and its response to environmental forcings. Here researchers will undertake a project born from a recent analysis by Behrenfeld et al. in which the authors interrogate the basis of the common phenomenon of co-variations in the light-limited slope (ab) and light-saturated rate (Pb max) of photosynthesis. The implications of this phenomenon on PE relationships exceed those of the photoacclimatory responses, yet covariability in ab and Pb max has received relatively little attention and the physiological basis has remained undetermined. Covaritation in ab and Pb max results in little or no influence on the light saturation irradiance for photosynthesis (Ek). There is Ek-independent variability. Ek-independent changes in ab and Pb max are wholly unexpected if, as generally assumed, ab and Pmax are limited by separate aspects of photosynthesis and ab is relatively constant.
In this project, the researchers present an overview of the phenomenon of Ek-independent variability and propose a new explanation for this unique behavior. Our hypothesize is that this Ek-independent phenomenon is an expression of intracellular changes in demands for reductant versus ATP associated with specific metabolic pathways that shift in dominance at time scales of single diurnal periods to seasonal changes in nutrient-limited growth. These shifts in dominant metabolic pathways drive changes in electron flow between linear photosynthetic electron transfer (PSII to carbon reduction) and alternative pathways that rapidly transfer electrons from PSII back to O2 and in the process generate ATP.
The broader impacts include advancing our understanding of the fundamental processes of photosynthesis and will lead to improved estimates of global ocean primary production and its role in biologically-mediated carbon sequestration. It will also support the education and practical training of a graduate student.
