DYPHORA—a dynamic model for the rate of photosynthesis of algae

Experimental data obtained from different cultures of phytoplankton indicate that photosynthesis (P) depends on light intensity (I) in a dynamic way. Therefore, static P/I curves relating photosynthesis to the instantaneous light may not be adequate to describe the activity of algal cells in lakes or oceans where mixing can cause a complex pattern of light variation. The model DYPHORA (DYnamic model for the PHOtosynthetic Rate of Algae) describes the response of photosynthesis to light using two characteristic times, the response time to increasing light (τr), and the light inhibition decay time (τr). The model agrees well with available experiments if τr is chosen between 0.5 and 5 min, and τr, between 30 and 120 min. It explains the occurrence of the well-documented afternoon depression as well as the decrease of integrated long-term rates of photosynthesis with increasing light. Although the presented comparison of experimental data and model results cannot serve as a proof for DYPHORA in a strict sense, the structural relationship between P and I can nevertheless point out inadequacies in the common interpretation of static P/I relationships. The model can also serve as a tool to test hypotheses regarding the selective role of mixing in the competition between algal species.