Growth rate and temperature of freshwater phytoplankton from Morphology-based differences in the thermal response of freshwater phytoplankton.

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 (<i>E</i>_r), (ii) the presence of a break in the thermal response and (iii) the activation energy of the fall (<i>E</i>_f). The whole dataset (<i>N</i> = 563) showed an exponential increase (<i>E</i>_r ∼ 0.5), a break around 24°C and no temperature dependence after the breakpoint (<i>E</i>_f = 0). Contrasting thermal responses among MBFG were found. All groups showed positive activation energy (<i>E</i>_r &gt; 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.