Comparative growth and metabolism of gelatinous colonies of three cyanobacteria, Nostoc commune , Nostoc pruniforme and Nostoc zetterstedtii , at different temperatures

Summary The cyanobacterial genus Nostoc includes several species forming large spherical or sheet‐like gelatinous colonies of ecological importance in freshwater and semi‐terrestrial habitats. We tested differences in morphology, growth and metabolism across a range of temperatures (6–43 °C) of three colonial species of Nostoc collected and grown in ambient water from typical localities from Denmark and Sweden: the plume‐shaped Nostoc pruniforme , the rare blackberry‐shaped Nostoc zetterstedtii and the semi‐terrestrial, sheet‐like Nostoc commune . All three species grew and photosynthesised in water between 6 and 33 °C in our experiments but died at 43 °C. The optimum temperature of around 25 °C and the critical temperature of around 33 °C are markedly higher than mean and maximum temperatures in the majority of habitats of N. pruniforme and N. zetterstedtii, suggesting that their distribution does not reflect temperature preference directly. Although N. commune survives deep‐freezing and heating to 70 °C, sustained growth was restricted to 0–33 °C. Maximum growth rates were relatively high for N. pruniforme and N. commune (doubling time of 13–15 days) and extremely low for N. zetterstedtii (doubling time of 2.4 years). Rates of photosynthesis, respiration and growth were markedly higher in alkaline water than in softwater, but N. pruniforme still grew much faster than N. zetterstedtii in the same water. Declines of growth and photosynthetic rates with increasing ratio of dry weight to surface area between the species and with increasing colony size reflect higher respiratory costs relative to resource uptake. We conclude that the three Nostoc species have similar temperature tolerance from 6 to 43 °C, despite large interspecific differences in rates of growth and photosynthesis, colony persistence and distribution.