SEASONAL-VARIATIONS IN P-I RESPONSES OF CHARA-HISPIDA L. AND POTAMOGETON-PECTINATUS L. FROM STREAM MEDITERRANEAN PONDS

The relationship between primary production and irradiance was analyze d over an annual cycle in the submerged macrophytes, Chara hispida and Potamogeton pectinatus, of two mediterranean stream ponds. The effect of temperature on photosynthesis was also studied. The population of P. pectinatus reached maximum production values of 19.67 mgO(2) g(-1) AFDW h(-1) in December at 20 degrees C. In summer and owing to the dev elopment of floating filamentous algae, P. pectinatus growth decreased . This can be observed in a decrease in production and chlorophyll con tent. At the end of autumn a 'self-pruning' mechanism in P. pectinatus caused increase of light penetration and new shoots were observed. C. hispida showed maximum production values of 10.86 mg O-2 g(-1) AFDW h (-1) in May. In summer, in agreement with temperature increase C. hisp ida fructifies and decays, increasing P. pectinatus growth and cover i n the same pond. Photoinhibition was observed in C. hispida in October , in agreement with a low radiation adaptation owing to an unusual dec rease in light penetration in the pond, caused by inputs of suspended material from a fire suffered in the watershed at the end of summer. V ariations in temperature had no effect on Pm/R ratio in P. pectinatus and decreased sharply from young to old tissue. The effect of temperat ure on the Pm/R ratio in C. hispida was significant. P. pectinatus sho wed great adaptation capacity to temperature fluctuations and light an d this adaptation is higher than in C. hispida, which is affected by t emperature increase and light penetration reduction. (C) 1998 Elsevier Science B.V.