Light-limited growth and photosynthetic characteristics of two planktonic desmid species

1. Staurastrum chaetoceras, originating from a eutrophic environment, and Cosmarium abbreviatum var. planctonicum, from an oligo-mesotrophic one, were grown at 20°C in continuous-flow culture under varied light conditions. 2. Maximum growth rate in S. chaetoceras was approximately 50% higher than in C. abbreviatum, corresponding to a higher photosynthetic capacity. 3. Higher dry weight values and dark respiration rates in C. abbreviatum (compared with S. chaetoceras) support the suggestion from growth-irradiance curves that C. abbreviatum has to invest a greater part of its photosynthetic energy in the construction and maintenance of specific cell components. 4. The differences in growth and photosynthetic parameters might be related to the presence of a copious mucilaginous cell envelope in C. abbreviatum; such an envelope is lacking in S. chaetoceras. 5. The possible ecological significance of these species-specific differences is discussed.     

Growth responses of planktonic desmid species in a temperature—light gradient

SUMMARY. 1. Isolates of twelve planktonic desmid species were tested for their growth response in batch culture, using an apparatus that generates crossed gradients of temperature and light intensity.
2. Up to 15°C, growth was mainly temperature-limited. At higher temperatures, there was an increasing effect of light limitation. Optimal growth temperatures were in the range 25–30°C.
3. Highest specific growth rates varied from 0.28 to 1.34 day⁻¹. Species with lowest growth rates originated from oligo-mesotrophic habitats, those with highest growth rates from eutrophic ones.
4. Ecophysiological aspects are discussed in some detail, as well as the significance of the experimental data for distributions in the field.