SEASONAL PHOTOSYNTHETIC AND RESPIRATORY RESPONSES OF RUPPIA-CIRRHOSA (PETAGNA) GRANDE TO CHANGES IN LIGHT AND TEMPERATURE

The photosynthetic and dark respiration rates of the macrophyte Ruppia cirrhosa from a Mediterranean coastal lagoon were examined across a range of temperature (10-40-degrees-C) and light (0-2300 muE m-2 s-1) conditions in the different stages of development. Plants were sampled in May, July, October and December (site temperatures ranged from 7 to 28-degrees-C). Total chlorophyll content in R. cirrhosa ranged between 738 +/-19 mg g-1 fresh weight (October) and 1060 +/- 18 mg g-1 fresh weight (May). Net photosynthetic rates reached maximum values (10.92 +/- 1.24 Mg O2 g-1 dry weight h-1) in spring and minimum values in autumn (5.8 +/- 0.85 mg 02 g-1 dry weight h-1). Saturation and compensation photon flux densities, Ik and Ic, reached maximum values in spring and early summer. High temperature (35 - 40-degrees-C) inhibition of photosynthesis was observed in May and December. Respiration rates always increased with temperature (p < 0.05) but the highest responses were found in May. Ratios of photosynthetic rates to respiration rates (Pn: R) were highest in winter and then declined until autumn, following biomass and age. Photosynthetic and respiratory responses of R. cirrhosa to temperature and light were affected by the environmental temperature at the site of collection and by the corresponding developmental stage. The photosynthetic and respiratory characteristics of R. cirrhosa indicate a species adapted to a wide range of light and temperature, which helps to explain its distribution in shallow, fluctuating environments such as coastal lagoons.