Leaf key traits of Erica arborea L., Erica multiflora L. and Rosmarinus officinalis L. co-occurring in the Mediterranean maquis

Leaf morphology and anatomy, water relations, leaf life-span, and gas exchange of Erica arborea L., Erica multiflora L. and Rosmarinus officinalis L. co-occurring in the Mediterranean maquis developing along the coast near Rome were analysed in the period from May 2000 through December 2001. The year 2001 was characterised by a severe drought period from the beginning of June to the middle of September (13.2 mm total rainfall, 32degreesC average maximum air temperature). The highest pre-dawn leaf water potential (Psi(pd) = -1.2 +/- 0.2 MPa) and relative water content (RWC = 87 +/- 4%) of E. arborea compared to the other two species were indicative of a high leaf water potential recovering capacity, allowing a sufficient photosynthetic activity (Pn = 2.9 +/- 0.4 mumol m(-2) s(-1)) during the severe drought period. On the contrary, R. officinalis showed 93% Pn rate decrease during drought with respect to the maximum rate. Moreover, the large Psi(pd) variation during the year (from -0.16 to -3.50 MPa) was indicative of a low recovery capacity, which might be related to its narrow root system. From a physiological point of view, E. multiflora had a similar trend to that of R. officinalis with a large Psi(pd) variation during the year and a low Psi(pd) value (-2.50 +/- 0.3 MPa) during the severe drought period. The correlation analysis carried out on morphological leaf traits for E. arborea, E. multiflora, R. officinalis and, by previous studies, for the other dominant shrub species of the Mediterranean maquis at the research site of Castelporziano (Quercus ilex L., Phillyrea latifolia L., Arbutus unedo L., Cistus incanus L.) indicated that variations in leaf mass per unit leaf area (LMA) were associated with variations in leaf tissue density (LTD), leaf life-span (LL), and leaf thickness (L). Discriminant analysis carried out on net photosynthesis (Pn), stomatal conductance (g(s)), transpiration rate (E), water relations (Psi, RWC), LMA, LL and L showed that g(s) and LL were the most discriminating leaf traits.