Respuesta plástica a la luz y al agua en cuatro especies mediterráneas del género Quercus (Fagaceae)

Light and water availability are two of the main factors that regulate growth and survival of Mediterranean woody plants. The objective of this study is to investigate the plastic response of seedlings of four Mediterranean Quercus species to these factors, as well as to determine what traits are more plastic to one or another factor. Our hypothesis was that physiological variables are more plastic than structural variables. We cultivated in controlled conditions seedlings of Quercus ilex ssp. ballota, Q. suber, Q. pyrenaica and Q. canariensis in three treatments of light (100, 27 and 3 % of incident light) and with abundant water. On late spring, watering was stopped for half of the seedlings, so there were two water treatments (irrigation versus no-irrigation) within each treatment of light. Several physiological traits were Studied: photosynthetic and respiration rate, light compensation and saturation points, stomatal conductance, water use and nitrogen use efficiency. We also evaluated different structural traits were studied Such as leaf area, specific leaf area, leaf nitrogen and carbon concentrations, and a chlorophyll index. Changes in water availability induced low plastic responses of structural traits, whereas responses of physiological traits were relatively higher. On the other hand, there were not significant differences in the plastic response of structural or physiological traits to changes in light availability. In these Mediterranean oak species, the higher response to light could be linked to a shade tolerance strategy and the low response to water (i.e., canalization) could be related to drought tolerant strategy, thus indicating that tolerance to low-resources may be attained through different strategies.