INTERACTIONS OF LIGHT AND NITROGEN ON PHOTOSYNTHESIS AND GROWTH OF THE MARINE MACROALGA ULVA-CURVATA (KUTZING) DE TONI

Ulva curvata (Kutzing) De Toni was cultivated outdoors at two nitrogen (ammonia) concentrations in combination with four light levels in order to determine the relationship of growth and photosynthesis under different levels of light and nutrients. The results showed that nitrogen concentration affects growth and photosynthesis only under optimal (200-500 muE.m-2.s-1) light conditions. Growth was always saturated at lower irradiance than was photosynthesis, independent of the nutrient regimes. Two major conclusions can be inferred from these results: first, whenever the growth of U. curvata is limited by the supply of inorganic nutrients rather than by the rate of photosynthesis, the plant will produce more photosynthetic products than can be used for growth or are required for respiration; and second, photosynthesis is only one of many processes involved in growth, and should not be considered as equivalent to growth. Our findings emphasize that light is an important factor controlling growth of this species, and that nitrogen would be limiting only at saturated light conditions.