Seasonal variations in P–I responses of Chara hispida L. and Potamogeton pectinatus L. from stream mediterranean ponds

Abstract

The relationship between primary production and irradiance was analyzed 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°C. In summer and owing to the development of floating filamentous algae, P. pectinatus growth decreased. This can be observed in a decrease in production and chlorophyll content. 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. hispida fructifies and decays, increasing P. pectinatus growth and cover in the same pond. Photoinhibition was observed in C. hispida in October, in agreement with a low radiation adaptation owing to an unusual decrease in light penetration in the pond, caused by inputs of suspended material from a fire suffered in the watershed at the end of summer. Variations in temperature had no effect on Pm/ R ratio in P. pectinatus and decreased sharply from young to old tissue. The effect of temperature on the Pm/ R ratio in C. hispida was significant. P. pectinatus showed great adaptation capacity to temperature fluctuations and light and this adaptation is higher than in C. hispida, which is affected by temperature increase and light penetration reduction.