INFLUENCE OF TEMPERATURE AND NITROGEN CONCENTRATION ON PHOTOSYNTHESIS OF DUNALIELLA-VIRIDIS TEODORESCO

The photosynthetic behaviour of Dunaliella viridis has been studied under a combination of three variables: irradiance (0-900-mu-mol m-2 s-1), temperature (15, 23, 31, 38, 42-degrees-C) and nitrogen concentration (0.05, 0.5, 1.5, 5, 10 mM NO3-) at a salinity of 2 M NaCl. The highest rates of photosynthesis have been found at 31-degrees-C and a nitrate concentration of 10 mM. There exists a synergistic effect between temperature and nitrogen availability on the photosynthesis of D. viridis; under nitrogen deficiency oxygen evolution is low, even null at high temperature. The interaction between these two variables of control occurs in a multiplicative way. There is also a general increase in photosynthetic pigments following the increase in nitrogen concentration in the culture medium. The normalization of net photosynthesis data in relation to chlorophyll a shows that nitrogen concentration makes an indirect control of the photosynthetic rate of D. viridis through the variation of pigment concentration. The study of the photosynthetic parameters shows that the slope (alpha) of the curves of photosynthesis and the light-saturated photosynthesis (P(max)) are controlled by more than one variable, including temperature and nitrogen availability.