© 2000 Heron Publishing—Victoria, Canada
Energy dissipation in drought-avoiding and drought-tolerant tree species
at midday during the Mediterranean summer
E. Martínez-Ferri (1, 2), L. Balaguer (1), F. Valladares (3), J. M. Chico (2) and E. Manrique (2)
1. Departamento Biología Vegetal I, Facultad de Biología, Universidad Complutense,
28040-Madrid, Spain / 2. Departamento Biología Vegetal II, Facultad de Farmacia, Universidad Complutense, 28040-Madrid, Spain / 3. Centro de Ciencias Medioambientales, C.S.I.C., Serrano 117, 28006-Madrid, Spain / Received March 11, 1999
Summary
Photosynthetic performance was monitored during two consecutive summers in four co-occurring evergreen Mediterranean tree
species growing on a south-facing rocky slope. In response to midday water stress, the drought-avoiding species Pinus halepensis Mill. exhibited marked stomatal closure (gs) but no changes in stem water potential (Ψs), whereas the drought-tolerant species Quercus coccifera L., Q. ilex ssp. ballota (Desf.) Samp. and Juniperus phoenicea L. displayed declines in midday gs and Ψs. The higher resistance to CO2 influx in needles of P. halepensis compared with the other species did not result in either a proportional increase in non-radiative dissipation of excess energy
or photo-inactivation of photosystem II (PSII). No significant differences were found among species either in the de-epoxidation
state of the xanthophyll cycle (DPS) or in the pool of its components on a total chlorophyll basis (VAZ). Despite contrasting
midday assimilation rates, the three drought-tolerant species all exhibited a pronounced drop in photochemical efficiency
at midday that was characterized by a decrease in the excitation capture efficiency of the open PSII centers. Although photoinhibition
was not fully reversed before dawn, it apparently did not result in cumulative photo-damage. Thus, the drought-avoiding and
drought-tolerant species employed different mechanisms for coping with excess light during the midday depression in photosynthesis
that involved contrasting midday photochemical efficiencies of PSII and different degrees of dynamic photoinhibition as a
photo-protective mechanism. These behaviors may be related to the different mechanisms employed by drought-avoiding and drought-tolerant
species to withstand water deficit.
Keywords:
chlorophyll fluorescence, Juniperus phoenicea, midday depression, Pinus halepensis, photo-protection, Quercus coccifera, Quercus ilex, xanthophyll cycle.
