Chlorophyll fluorescence parameters of three Mediterranean shrubs in a summer-autumn period in central Portugal

Abstract

The photosynthetic performance of Cistus crispus, Centaurea africana and Thymus villosus, three shrubs of the Mediterranean-type maquis vegetation of Central Portugal, were studied between July and December 2003 by means of in vivo chlorophyll a fluorescence measurements. In C. africana total leaf decay occurred between August and October, in T. villosus no clear pattern of variation of the basal fluorescence (Fo) was observed, and in C. crispus an increase of this parameter was observed in late autumn. In all species, the limitation to photosynthesis by photoinhibition and the contribution of non-reversible processes to total photoinhibition were more pronounced in the summer than in the autumn. However, a pronounced decrease of the effective quantum yield of photosystem 2 (ΦPS2) was found in late autumn, probably due to a decrease of the carboxylation efficiency of the Calvin-Benson cycle, which was also supported by a parallel decrease of the photochemical quenching coefficient (qP).