Effect of temperature on photosynthesis‐light response and growth of four phytoplankton species isolated from a tidal freshwater river

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Abstract
Three cyanobacteria (Microcystis aeruginosaKütz. emend. Elenkin,Merismopedia tenuissimaLemmermann, andOscillatoriasp.) and one diatom (Aulacoseira granulatavar.angustissimaO. Mull. emend. Simonsen) were isolated from the tidal freshwater Potomac River and maintained at 23° C and 40 μmol photons·m−2·s−1on a 16:8 L:D cycle in unialgal culture. Photosynthetic parameters were determined in nutrient‐replete cultures growing exponentially at 15, 20, 25, and 30° C by incubation with14C at six light levels.P Bmaxwas strongly correlated with temperature over the entire range for the cyanobacteria and from 15 to 25° C forAulacoseira, withQ10ranging from 1.79 to 2.67. The α values demonstrated a less consistent temperature pattern. Photosynthetic parameters indicated an advantage for cyanobacteria at warmer temperatures and in light‐limited water columns.P BmaxandIkvalues were generally lower than comparable literature and field values, whereas α was generally higher, consistent with a somewhat shade acclimated status of our cultures. Specific growth rate (μ), as measured by chlorophyll change, was strongly influenced by temperature in all species.Oscillatoriahad the highest μ at all temperatures, joined at lower temperatures byAulacoseiraand at higher temperatures byMicrocystis.Values of μ forAulacoseirawere near the low end of the literature range for diatoms consistent with the light‐limited status of the cultures. The cyanobacteria exhibited growth rates similar to those reported in other studies.Q10for growth ranged from 1.71 forAulacoseirato 4.16 forMicrocystis.Growth rate was highly correlated withP Bmaxfor each species and the regression slope coefficients were very similar for three of the species.