Leaf anatomy, inclination, and gas exchange relationships in evergreen sclerophyllous and drought semideciduous shrub species

There are significant differences in leaf life-span among evergreen sclerop hyllous species and drought semideciduous species growing in the Mediterran ean maquis. Cistus incanus, which has a leaf life-span of four-eight months , was characterised by the highest net photosynthetic rates (PN). while Que rcus ilex and Phillyrea latifolia, which maintain their leaves two-three an d two-four years, respectively, had a lower PN- The longer leaf life-span o f the two evergreen sclerophyllous species may be justified to cover the hi gh production costs of leaf protective structures such as cuticle, hairs, a nd sclereids: cuticle and hairs screen radiation penetrating into the more sensitive tissues, and sclereids have a light-guiding function. Q. ilex and P. latifolia have the highest leaf mass/area ratio (LMA = 209 g m(-2)) and a mesophyll leaf density (2065 cells per mm(2) of leaf cross section area) about two times higher than C. incanus. In the typical evergreen sclerophy llous species the steepest leaf inclination (alpha = 56 degrees) reduces 42 % of radiation absorption, resulting in a reduced physiological stress at l eaf level, particularly in summer. C. incanus, because of its low leaf life -span, requires a lower leaf investment in leaf protective structures. It e xhibits a drastic reduction of winter leaves just before summer drought, re placing them with smaller folded leaves. The lower leaf inclination (alpha = 44 degrees) and the lower LMA (119 g m(-2)) of C. incanus complement phot osynthetic performance. Water use efficiency (WUE) showed the same trend in Q. ilex, P. latifolia, and C. incanus, decreasing 60% from spring to summe r, due to the combined effects of decreased CO2 uptake and increased transp irational water loss.