EFFECTS OF TEMPERATURE AND IRRADIANCE ON THE GROWTH OF 2 FRESH-WATER PHOTOSYNTHETIC CRYPTOPHYTES

Effects of light and temperature on growth of two freshwater photosynt hetic cryptophytes of different cell size were studied in batch cultur es. For the smaller Cryptomonas 979/67, Steele's model and equation of Platt et al. described the relationship between growth rate and photo n flux density (PFD), whereas a hyperbolic tangent function gave a bet ter fit for the larger Cryptomonas 979/62. Maximum growth rates given by the three models were consistent with each other, but the hyperboli c tangent function gave slightly lower estimates. Maximum growth rates in relation to temperature were well described for both species by th e model of Logan et al. The optimum temperature for growth for Cryptom onas 979167 was ca. 24.5-degrees C and 19.0-degrees-C for Cryptomonas 979/62. The lethal temperatures were 30.4-degrees-C and 23. 1-degrees- C for 979/67 and 979/62, respectively. The estimated maximum growth ra tes were 1.38 div. .day-1 for Cryptomonas 979/67 and 0.87 div. .day-1 for Cryptomonas 979/62. There were interspecific differences in photoa daptation strategies, as Cryptomonas 979/67 required relatively high P FDs to show net growth, whereas Cryptomonas 979/62 grew at lower irrad iances. Cryptomonas 979/67 showed photoinhibition soon after the satur ation point, but Cryptomonas 979/62 tolerated a much wider range of ir radiance. From their growth responses to light, Cryptomonas 979/67 app ears to be a stenotopic and Cryptomonas 979/62 a eurytopic strain.