M. Menendez et J. Penuelas, SEASONAL PHOTOSYNTHETIC AND RESPIRATORY RESPONSES OF RUPPIA-CIRRHOSA (PETAGNA) GRANDE TO CHANGES IN LIGHT AND TEMPERATURE, Archiv fur Hydrobiologie, 129(2), 1993, pp. 221-230
The photosynthetic and dark respiration rates of the macrophyte Ruppia
cirrhosa from a Mediterranean coastal lagoon were examined across a r
ange of temperature (10-40-degrees-C) and light (0-2300 muE m-2 s-1) c
onditions 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 betwee
n 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 aut
umn (5.8 +/- 0.85 mg 02 g-1 dry weight h-1). Saturation and compensati
on photon flux densities, Ik and Ic, reached maximum values in spring
and early summer. High temperature (35 - 40-degrees-C) inhibition of p
hotosynthesis was observed in May and December. Respiration rates alwa
ys increased with temperature (p < 0.05) but the highest responses wer
e found in May. Ratios of photosynthetic rates to respiration rates (P
n: R) were highest in winter and then declined until autumn, following
biomass and age. Photosynthetic and respiratory responses of R. cirrh
osa to temperature and light were affected by the environmental temper
ature at the site of collection and by the corresponding developmental
stage. The photosynthetic and respiratory characteristics of R. cirrh
osa indicate a species adapted to a wide range of light and temperatur
e, which helps to explain its distribution in shallow, fluctuating env
ironments such as coastal lagoons.