Water relations and photosynthetic performance of fruticose Lichens from the semiarid Southeast of Spain

The lichen species Teloschistes lacunosus (RUPR.) SAV, and Ramalina bourgea na NYL. are characteristic of the semiarid southeast Iberian Peninsula. The se species showing different distribution patterns and ecological requireme nts, were collected at the coast (R. bourgeana) and in the inland (T. lacun osus). Laboratory experiments revealed that net photosynthesis (NP) and dar k respiration (DR) responses to temperature differed between both species. Optimal temperatures of NP were higher in T. lacunosus than in R. bourgeana at optimal thallus water content at the various photosynthetic photon flux density (PPFD) levels. In the upper temperature range studied (20-25 degre es C), R. bourgeana proved to be less efficient than T. lacunosus. In both species, lower and upper temperature compensation points were below 0 degre es C and above 30 degrees C, for moderate and high PPFD levels, respectivel y. At high temperatures and high thallus water content, T. lacunosus showed lower DR rates than R. bourgeana. NP response to PPFD also showed differen ces between both species. The light compensation points were high in both s pecies for temperatures above 20 degrees C (at 20 degrees C around 50 mu mo l m(-2)s(-1) in T. lacunosus, and around 60 mu mol m(-2)s(-1) in R. bourgea na). Light saturation of NP was higher in T. lacunosus at all temperatures in the experiments. In T. lacunosus, the value was below 1200 mu mol m(-2)s (-1) at 0-15 degrees C, but at temperatures above 15 degrees C, it was abov e 1200 mu mol m(-2)s(-1). In R. bourgeana the values were always below 1200 mu mol m(-2)s(-1). In both species, NP was strongly depressed at supraopti mal water content. The physiological differences observed between R. bourge ana and T. lacunosus, and their relation to the distribution patterns of th ese lichens are discussed.