Correlation between leaf age and other leaf traits in three Mediterranean maquis shrub species: Quercus ilex, Phillyrea latifolia and Cistus incanus

The anatomical and morphological leaf traits as well as leaf inclination and orientation per different leaf age cohort of Quercus ilex, Phillyrea latifolia and Cistus incanus growing in the Mediterranean maquis along Rome's coast-line (Italy) were investigated. Specific leaf weight (SLW), total leaf thickness (L), leaf density index and leaf inclination (alpha) changed according to leaf age. The maximum values were measured at full leaf expansion, underlining the strong influence of alpha on the reduction of solar radiation incident on leaf surface and the importance of the received solar radiation by leaf structure during leaf age. C. incanus summer leaves had the lowest surface area, the highest SLW (15 +/- 2 mg cm(-2)) and L (244 +/- 15 mu m) with respect to winter leaves, reducing the evaporative leaf surface during drought. Older leaves of 2-4 years Q. ilex and P. latifolia, shaded by new leaves had lower a: than 1 year old leaves. alpha is a linear function of SLW. By the seasonal leaf dimorphism and the characteristic leaf folding the adjustment of leaf inclination angle from -37 degrees in winter leaves to + 44 degrees in summer leaves increased reduction of incident solar radiation during drought. Leaf folding may be related to the less xeromorphic leaf structure of C. incanus. The index of xeromorphism, measured at full leaf expansion and resulting from the surface area of the polygon plotted joining the value of the seven considered xeromorphic leaf traits in the radar graph, is the highest in P. latifolia (0.88), and the lowest in C. incanus (0.44). (C) 2000 Elsevier Science B.V. All rights reserved.