Physiological responses of tagasaste to a progressive drought in its native environment on the Canary Islands

Diurnal courses of gas exchange, chlorophyll fluorescence, shoot water potential (Psi) and leaf relative water content (RWCleaf) were recorded in Chamaecytisus proliferus (L. fil.) Link ssp. proliferus var. palmensis (Christ) (tagasaste) growing in natural conditions in the North-West slope of Tenerife, Canary Islands. During the studied period (April-July 2000), the soil relative water content (RWCsoil) progressively decreased, while the air vapour pressure deficit increased. As a consequence a decrease in Psi and RWCleaf took place as well as a decrease in stomatal conductance (g(s)) and CO2 assimilation rate (A). These characteristics, typical of an anisohydric plant, allowed this species to endure a mild drought. Photochemical efficiency of PSII (phi(PSII)) followed the inverse pattern to that observed for the photosynthetic photon flux density (PPFD), decreasing at midday and recovering during the late afternoon. This recovering at the end of each day, and the constant values of the maximum quantum yield of PSII photochemistry (F-v/F-m) during the studied period, indicate that there was no permanent damage to the photosynthetic apparatus due to mild water stress. (c) 2004 Elsevier B.V. All rights reserved.