title: Seasonal changes in net photosynthesis rates and photosynthetic capacity in leaves of Cistus salvifolius, a European mediterranean semi-deciduous shrub.
abstract: During five different periods between Nov. 1982 and Aug. 1983, the diurnal patterns exhibited in photosynthetic CO2uptake and stomatal conductance were observed under natural conditions on twigs of Cistus salvifolius, a Mediterranean semi-deciduous shrub which retains a significant proportion of its leaves through the summer drought. During the same periods, net photosynthesis at saturating CO2partial pressure was measured on the same twigs as a function of irradiance at different temperatures. From these data, photosynthetic capacity, defined here as the CO2- and light-saturated net photosynthesis rate, was obtained as a function of leaf temperature. C. salvifolius is a winter growing species, shoot growth being initiated in Nov. and continuing through May. Photosynthetic capacity was quite high in Nov., March and June, exceeding 40 μmol m-2s-1at optimum temperature. In Dec., photosynthetic capacity was somewhat reduced, perhaps due to low night-time temperatures (<5°C) during the measurement period. In Aug., capacity in oversummering shoots at optimum temperature fell to less than 8 μmol m-2s-1, due to water trees and perhaps leaf aging. Seasonal changes in maximal photosynthetic rates under ambient conditions were similar, and like those found in co-occurring evergreen sclerophylls. Like the evergreens, Cistus demonstrated considerable stomatal control of transpirational water loss, particularly in oversummering leaves. During each measurement period except Aug. when capacity was quite low, the maximum rates of net photosynthesis measured under ambient conditions were less than half the measured photosynthetic capacities at comparable temperatures, suggesting an apparent excess nitrogen investment in the photosynthetic apparatus.
authors.affiliation: Systems Ecology Research Group, San Diego State University, 92182, San Diego, CA, USA.
authors.forename: P C
authors.initials: PC
authors.lastname: Harley
authors.affiliation: Systems Ecology Research Group, San Diego State University, 92182, San Diego, CA, USA.
authors.forename: J D
authors.initials: JD
authors.lastname: Tenhunen
authors.affiliation: Lehrstuhl für Botanik II, Universität Würzburg, Mittlerer Dallenbergweg 64, D-8700, Würzburg, Federal Republic of Germany.
authors.forename: W
authors.initials: W
authors.lastname: Beyschlag
authors.affiliation: Lehrstuhl für Botanik II, Universität Würzburg, Mittlerer Dallenbergweg 64, D-8700, Würzburg, Federal Republic of Germany.
authors.forename: O L
authors.initials: OL
authors.lastname: Lange
keywords: Cistus; Drought deciduous shrubs; Mediterranean vegetation; Photosynthesis