Abstract
The thermal response of maximum growth rate in morphology-based functional groups (MBFG) of freshwater phytoplankton is analysed. Contrasting an exponential Boltzmann-Arrhenius with a unimodal model, three main features were evaluated: (i) the activation energy of the rise (E(r)), (ii) the presence of a break in the thermal response and (iii) the activation energy of the fall (E(f)). The whole dataset (N = 563) showed an exponential increase (E(r) ∼ 0.5), a break around 24°C and no temperature dependence after the breakpoint (E(f) = 0). Contrasting thermal responses among MBFG were found. All groups showed positive activation energy (E(r) > 0), four showed no evidence of decline in growth rate (temperature range = 0-35°C) and two presented a breakpoint followed by a sharp decrease in growth rate. Our results evidenced systematic differences between MBFG in the thermal response and a coherent response significantly related to morphological traits other than size (i.e. within MBFG). These results provide relevant information for water quality modelling and climate change predictions.