© 2005 Heron Publishing—Victoria, Canada
Shade tolerance, photoinhibition sensitivity and phenotypic plasticity of Ilex aquifolium in continental Mediterranean sites
Fernando Valladares (1, 2), Sagrario Arrieta (3), Ismael Aranda (4), David Lorenzo (4), David Sánchez-Gómez (1), David Tena (1), Francisco Suárez (3) and José Alberto Pardos (5)
1. Centro de Ciencias Medioambientales, CSIC, Serrano 115 dpdo, E-28006 Madrid, Spain / 2. Corresponding author (valladares@ccma.csic.es) / 3. Departamento de Ecología, Facultad de Ciencias, Universidad Autónoma de Madrid, E-28049 Madrid, Spain / 4. INIA, Ctra. de La Coruña km 7.5, E-28040 Madrid, Spain / 5. Escuela Técnica Superior de Ingenieros de Montes, Universidad Politécnica de Madrid, E28040 Madrid, Spain / Received July 14, 2004; accepted December 4, 2004; published online June 1, 2005
Summary
Shade tolerance, plastic phenotypic response to light and sensitivity to photoinhibition were studied in holly (Ilex aquifolium L.) seedlings transported from the field to a greenhouse and in adult trees in the field. All plants were growing in, or
originated from, continental Mediterranean sites in central Spain. Seedlings tolerated moderate but not deep shade. Mortality
was high and growth reduced in 1% sunlight. Survival was maximal in 12% sunlight and minimal in full sunlight, although the
relative growth rate of the seedlings surviving in high light was similar to that of plants in moderate shade. Maximum photochemical
efficiency at predawn was significantly lower in sun plants than in shade plants in the field, revealing chronic photoinhibition
that was most pronounced in winter. Plasticity in response to available light varied according to the variable studied, being
low for photosynthetic capacity and stomatal conductance, and high for specific leaf area, root:shoot ratio and leaf area
ratio, particularly in seedlings. Differences in water relations and hydraulic features between sun and shade plants in the
field were marginal. High water potential at the turgor loss point of field-grown plants suggested that holly is sensitive
to drought during both the seedling and the adult stage. Low relative growth rates in both high and low light with low physiological
plasticity in response to light indicate the existence of a stress-tolerance mechanism. We conclude that holly is a facultative
understory plant in areas of oceanic and relatively mild climate, but an obligate understory plant in dry continental areas
such as the study site. The impact of abandonment of traditional management practices and climate change on these Mediterranean
populations is discussed.
Keywords:
acclimation, holly, high light stress, photosynthesis, relative growth rate, seedlings, sun and shade, survival, water relations.
