How light and temperature interact to determine growth in phytoplankton: A synthesis

Background/Question/Methods

Temperature and light are primary controls of autotroph physiology, population growth, community structure, and ecosystem function. For the phytoplankton that dominate production in pelagic systems, we have a poor understanding of how temperature modulates the effects of light limitation, and how light limitation alters the metabolic scaling relationships driven by temperature. Here we investigate these questions using a synthesis of laboratory experiments measuring species-specific growth across crossed gradients of light and temperature. 

Results/Conclusions

We find that the temperature scaling of growth is strongly altered by light limitation, such that light-limited growth rate has zero or weak increase with temperature, in contrast to the strong increase of growth with temperature under light sufficiency. We also find that photoinhibition of growth is ameliorated by increasing temperature. Species-specific thermal optima shift as a function of light availability, such that the optimal temperature for growth declines when light is limiting or is in excess. We also analyze marine/freshwater differences and taxonomic effects. These results imply that metabolic scaling relationships are strongly affected by resource limitation, with consequences for ecosystem function across changing temperatures, while community structure will also be altered by light-temperature interactions in a way that is somewhat predictable.