| Interactions between light intensity, temperature, and nitrate (NO(,3)('-)) availability on steady-state rates of growth, physiological processes, and levels of chemical constituents of the red alga Gracilaria tikvahiae (Gigartinales) were studied using factorial design experiments in outdoor, continuous-flow seawater cultures. Between 15 and 20(DEGREES)C, the maximum growth rate ((mu)(,max)) of G. tikvahiae was depressed by temperature and below 15(DEGREES)C, G. tikvahiae did not grow. After transfer of G. tikvahiae from field seawater temperature (22(DEGREES)C) to 15(DEGREES)C, a nine day lag period occurred before growth ensued. During this lag period, levels of carbon, nitrogen, protein and carbohydrate increased, suggesting that G. tikvahiae acclimates to low temperatures by increasing quotas of these cellular constituents. Between 20 and 30(DEGREES)C, G. tikvahiae utilized maximum levels of light intensity for growth and photosynthesis whereas at 15(DEGREES)C, significant photoinhibition of these processes occurred at high light intensities. Maximum values of growth and the photosynthesis:respiration ratio occurred at 25(DEGREES)C. Levels of chlorophyll-a, R-phycoerythrin, protein and nitrogen in G. tikvahiae varied inversely with light intensity; conversely, activity of ribulose-1,5-biphosphate carboxylase varied directly with light intensity. This biochemical light acclimation maximizes the photosynthetic capacity of G. tikvahiae to a particular light intensity. NO(,3)('-) limitation depressed rates of growth and photosynthesis in high light intensity, low NO(,3)('-) treatments. Two nitrogen reserves, tissue NO(,3)('-) and R-phycoerythrin, supported growth of the N-limited G. tikvahiae during an initial 19 day growth period. Overall, a high intercorrelation (0.87 < r < 0.96) between rates of growth, photosynthesis, NO(,3)('-) uptake, and dark respiration suggests that highly balanced growth of G. tikvahiae occurs over a broad environmental range of light, temperature and NO(,3)('-) availability--a physiological profile that accounts for the ecological success of G. tikvahiae. |
