Stochastic parallel processing can shape photosynthesis–irradiance curves in phytoplankton—the Q model

Abstract

A mechanistic model was formulated that describes the rate of photosynthesis based on an analogy with queuing systems of operational research. The parallel electron processing capacity of the plastoquinone pool was hypothesized to be the key element in the photosynthetic electron transport chain, determining the process of light saturation for phytoplankton. The state of the plastoquinone pool was described mathematically by a continuous-time Markov chain. The model assumes that traditional photosynthesis measurements using incubation under constant irradiance can be regarded as stochastic equilibria. The model was tested on a set of photosynthesis–irradiance measurements taken in Lake Balaton (Hungary). It clearly outperformed the two most common empirical photosynthesis–irradiance models used in limnology by delivering the best-fit in most cases. Thus, the traditional limnological practice of choosing the right empirical, two-parameter photosynthesis–irradiance model that produces the best-fit can be replaced by simple calibration of three parameters, including a new one describing the degree of parallelism in the photosynthetic units. This parameter was found to specify the curvature of the photosynthesis–irradiance function.