Interactive effects of light and nutrients shape phytoplankton thermal traits.

The variable character of aquatic systems forces organisms to constantly adjust to their changing environment. We investigated how resource availability shapes the temperature sensitivity of growth for the freshwater phytoplankton species Scenedesmus armatus (Chodat). We used a gradient design of light and nutrients, to assess their interdependent effects on numerous thermal traits, determined from thermal performance curves (TPCs). Building on previous studies that demonstrated resource-dependent temperature sensitivity in growth for a single resource type, we advance this understanding by revealing the interdependent effects of multiple resources on thermal traits, using response surfaces. We showed that most resource effects on thermal traits highly depend on the availability of other resource that can even change the direction of the effect, and that thermal traits can differ in their resource dependence. Our study provides important knowledge of how organisms cope in their changing and multifactorial environment, especially in the face of climate warming.