Differences in biomass allocation patterns between saplings of two co-occurring Mediterranean oaks as reflecting different strategies in the use of light and water

Abstract

Production and biomass allocation patterns, the growth rates of aboveground biomass, and crown traits were examined in saplings of the deciduous Quercus faginea and the evergreen Q. ilex to determine whether differences in these traits might account for the greater mortality during periods of drought undergone by Q. faginea. Strong differences were observed in almost all the traits analyzed, which suggests that the two species use different strategies to cope with the main limiting factors for woody seedling establishment in Mediterranean environments: excess light and low water availability. In Q. faginea, sapling design seems to be oriented to maximize light capture and, hence, leaf productivity during the short life span of the leaf biomass. Thus, the seedlings of Q. faginea showed crown traits that permit self-shading to be minimized: longer shoots with more spaced leaves that result in lower leaf area index than in Q. ilex. In addition, the larger area per unit leaf biomass in Q. faginea leads to a larger interceptive leaf area per unit plant mass and to higher light capture. These characteristics imply higher investments in woody tissues (SWR) that permit the plants to support a wide canopy and facilitate water transport to meet the strong transpiratory demands of a canopy with such characteristics. By contrast, in Q. ilex, saplings are apparently designed to guarantee leaf survival against temperature extremes and photoinhibition through avoidance of excessive radiation.