Going for the slow burn: why should possession of a low maximum growth rate be advantageous for microalgae?

Abstract

Background: Phytoplankton show a wide range of maximum growth rates (μmax), with no obvious advantage to having a low μmax. Aims: To explore advantages for phytoplankton in having μmax values commensurate with the rate of nutrient supply in their environment, making use of a mechanistic model describing their growth. Methods : In contrast with the typical construction of quota-based models of microalgal growth, which scale the maximum nutrient uptake rate to μmax, a more realistic description of excess nutrient transport capacity endows organisms of lower μmax with a competitive advantage for nutrient acquisition. This, in turn, enables the retention of a higher organismal nutrient status at low-nutrient concentrations. Thence low μmax organisms may be expected to have lower intrinsic death rates, and also faster response times to capitalise on nutrient spikes. Results: Of the traits modelled, the lowering of death rate appears the most important, enabling cells of low μmax to out-compete their high μmax counterparts at low-nutrient concentration. An ability to recover more rapidly from nutrient stress is of lesser importance, and is unable to counter differences in μmax. Conclusions: Descriptions of features such as those modelled define properties of plankton functional types and also provide trade-off characteristics for placement within models considering emergent properties of plankton communities.