In situ comparison of Daily Photosynthetic Activity Patterns of Saxicolous Lichens and Mosses in Sierra de Guadarrama. Central Spain

Abstract

Diurnal time courses ofin situ photosynthetic acñvity oflichens and mosses growing on a granitic boulder in Sierra de Guadarrama, central Spain, were measured during five days in October, 1993. A portable chlorophyll fluorometer was used for assessing photosynthetic activity offour lichen and two bryophyte species together with photosynthetic photon flux density (PPFD) incident at the thallus surface and thallus temperature. The quantum efficiency of photosystem 11 (PSII; AF/Fm'), and the apparent electrón transpon rate through PSIl (AF/Fm' X PPFD) were calculated. The weather changed from wet to dry conditions during the period of measurements. Exposure- and species-related differences in the photosynthetic performance were observed. Both moss species, Hedwigia ciliata and Grimmia pulvinata, showed no sign of thallus drying and the photochemical efficiency of both species was mainly controlled by the diel patterns of PPFD. In contras!, water loss was the majar limiting factor for metabolic activity in the lichen species. Exposure- and species-related changes in thallus color indicating water loss occurred as early as on 18 October in Umbilicaria spodochroa and with a 24-hr-delay in Lasallia hispánica and Umbilicaria grísea (19 October). In Lasallia pustulata thallus color changes were visible only on 20 October when dry weather induced severe dehydration in all lichen species. Within the same species, different microhabitat resulted in a different physiological performance depending on water balances as well as on PPFD conditions. The data demónstrate the potential of fie Id measurements of chlorophyll a fluorescence as a non-intrusive tool for the analysis of the in situ photosynthetic performance of poikilohydric organisms without altering rates of water loss and uptake, which are always crucial in the photosynthetic performance of poikilohydric organisms under natural conditions.