LEAF MORPHOLOGY, LEAF CHEMICAL-COMPOSITION AND STEM XYLEM CHARACTERISTICS IN 2 PISTACIA (ANACARDIACEAE) SPECIES ALONG A CLIMATIC GRADIENT

Leaf and stem xylem features in Pistacia lentiscus (an evergreen shrub ) and P. terebinthus (a deciduous shrub) were analysed along an Atlant ic-Mediterranean gradient: which is characterised by a variation of ra infall and winter temperature. Leaf features were foliage area of 3-ye ar-old shoots (FA), leaflet area (LA), specific mass (SLM), thickness (LTh), density (LD), and chemical composition on a dry weight basis (N , P, cellulose Cel, hemicellulose Hcel, and lignin Lig). Stem traits r eferred to xylem anatomy: mean vessel diameter of the 25 largest vesse ls (MxD), vessel element length (VEL), number of vessels per xylem cro ss section area unit (VD) and the ratio xylem/foliage surface of shoot s (HV). Comparisons of traits have been made both at an interspecific and at an intraspecific level, this latter by analysing how these trai ts respond to variations of precipitation and winter temperature. P. t erebinthus showed higher FA, LA, MxD, N and Cel, but lower SLM, LTh, H cel, VD and HV than P. lentiscus. Both species showed opposite respons es of LTh to the reduction of mean minimum January temperature, decrea sing in the former and increasing in the latter. In Ft lentiscus VD in creased and VEL decreased when winter temperature became colder, while VD decreased and N increased towards the arid part of the gradient. I t is suggested that leaf habit plays an important role in determining the function of species and their response to the climatic gradient.