Comparative protective strategies of Cistus albidus and Quercus ilex facing photoinhibitory winter conditions

Is tree shelter protection an effective complement to weed competition management in improving the morpho-physiological response of holm oak planted seedlings?

“…Cold stress may affect the photoinhibition processes in Mediterranean plants either by cold wind or by cold-induced reduction of water absorption (Oliveira & Peñuelas 2004, Corcuera et al 2005. According to previous studies (Oliveira & Peñuelas 2002) a significant reduction in the maximum photochemical efficiency (Fv/Fm) was observed for non-sheltered seedlings. This decrease was linked to a significant reduction in the efficiency of electron transport (ETo/ABS), as well as an increase in the energy dissipation rate at the PSII antenna (DIo/ABS).…”

Implications of opposite phyllotaxis for light interception efficiency of Mediterranean woody plants

“…In a comparison of three Mediterranean shrubs of the genera Salvia and Cistus, transpiration was found not enough to overcome heat loads during the summer, and morphological features such as small and folded leaves were crucial to cope with heat stress (Szwarcbaum 1982). Similarly, steep leaf angles were found important in Mediterranean plants for avoidance of photoinhibition (Oliveira and Peñuelas 2002;Valladares and Pearcy 1997;Werner et al 1999) and for a more efficient distribution of light among all the foliage units due to enhanced light penetration to lower leaves (Valladares and Pearcy 1998). Species with spiral leaves were found to have steeper leaves than species with opposite phyllotaxis in our study, so we conclude that spiral phyllotaxis has potential ecological advantages not only in low light, since it allows for high Ea for a given investment in supporting biomass, but also in high light, since it allows for a more uniform illumination of the foliage units, as both prevent photoinhibition of upper leaves and maximizes whole crown photosynthesis.…”

“…The natural range of variation of internode length found in different shoots and individuals of each species studied had a larger effect on Ea than the natural range of leaf angle elevation. Leaf elevation angle has been shown to influence significantly light capture in a number of species and environmental conditions (McMillen and McClendon 1979;Niinemets and Fleck 2002;Oliveira and Peñuelas 2002;Valladares and Pearcy 1998), but this influence has been compared with that of other architectural traits only occasionally (Herbert 1996;Pearcy and Valladares 1999). In a comparative survey of the crown architecture of 38 perennial species of Australia, Falster and Westoby (2003) found that self-shading, rather than leaf angle, explained most of the variance between species in Ea, which was in turn primarily determined by leaf size.…”

Effects of moderate shade and irrigation with eutrophicated water on the nitrogen economy of Mediterranean oak seedlings

“…Therefore, the addition of N with irrigation water may promote luxury consumption and accumulation of N in plant tissues for future use (Chapin et al, 1990), as suggested above. Shade may have enhanced growth of the evergreens by two mechanisms: firstly, moderate shade reduces photoinhibition (Castro-Dı´ez et al, 2006;Valladares et al, 2005), but this process has been reported to have little effect on the whole-plant carbon gain in Mediterranean trees and shrubs (Oliveira and Pen˜uelas, 2002;Valladares et al, 2005;Werner et al, 2001). Secondly, shade reduces evapotranspiration and increases soil moisture (Holmgren, 2000;Rey-Benayas et al, 2005), suggesting again that growth is limited by water stress.…”