Comparative ecophysiology of Quercus suber L. and other accompanying oak species in Dehesa systemseffects on resource use efficiency in photosynthesis

Resumen

Quercus suber L. is a widespread species, whose distribution in central-western Spain coincides with the area of dehesas, a typical woody formation characterized by the presence of scattered trees with open pasture areas. In this region, Q. suber coexists with other several tree and shrub species. Water and nutrient shortages limit plant productivity in these Mediterranean areas, and competition among tree species for these limiting resources may severely restrict growth and productivity. Ecophysiological adaptations are thus extremely important in determining resource use efficiency and the competitive ability of the different species. Differences in leaf longevity have been often shown to be a determinant of gas-exchange patterns in tree species. Maximum gas-exchange rates in young leaves tend to decrease with increases in leaf longevity. Additionally, leaf ageing in evergreen species is associated with reduced stomatal conductances and CO, assimilation rates, even under favourable conditions during spring. These effects of long leaf longevity on photosynthesis are probably responsible for the slower growth rates usually associated with the evergreen habit. In this study we compare leaf life span and the gas-exchange patterns of four deciduous and evergreen oak species typical of the dehesa region in Central-Western Spain. Leaf life span in Q. suber is shorter than in other evergreen species. The gas-exchange rates of young leaves and leaf morphology characteristics of Q. suber are thus intermediate between deciduous and evergreen. Q. suber appears as an evergreen species because most of its leaves survive during the winter following their first growing season until immediately before the appearance of the following leaf cohort in spring. Its leaves may be thus classified as overwintering, rather than truly perennial, and overlapping between different leaf cohorts is very low. Accordingly, most of the leaf biomass of Q. Heber during spring is composed of young leaves with high gas-exchange rates and nitrogen use efficiency.