Principles of the light-limited chemostat: theory and ecological applications.

Light is the energy source that drives nearly all ecosystems on planet Earth. Yet, light limitation is still poorly understood. In this paper, we present an overview of the principles of the light-limited chemostat. The theory for light-limited chemostats differs considerably from the standard theory for substrate-limited chemostats. In particular, photons cannot be mixed by vigorous stirring, so that phototrophic organisms experience the light-limited chemostat as a heterogeneous environment. Similar to substrate-limited chemostats, however, light-limited chemostats do reach a steady state. This allows the study of phototrophic microorganisms under well-controlled light conditions, at a constant specific growth rate, for a prolonged time. The theory of the light-limited chemostat is illustrated with several examples from laboratory experiments, and a variety of ecological applications are discussed.