Leaf morphology, leaf chemical composition and stem xylem characteristics in two 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 Atlantic-Mediterranean gradient: which is characterised by a variation of rainfall and winter temperature. Leaf features were foliage area of 3-year-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 referred to xylem anatomy: mean vessel diameter of the 25 largest vessels (MxD), vessel element length (VEL), number of vessels per xylem cross section area unit (VD) and the ratio xylem/foliage surface of shoots (HV). Comparisons of traits have been made both at an interspecific and at an intraspecific level, this latter by analysing how these traits respond to variations of precipitation and winter temperature. P. terebinthus showed higher FA, LA, MxD, N and Cel, but lower SLM, LTh, Hcel, VD and HV than P. lentiscus. Both species showed opposite responses of LTh to the reduction of mean minimum January temperature, decreasing in the former and increasing in the latter. In Ft lentiscus VD increased and VEL decreased when winter temperature became colder, while VD decreased and N increased towards the arid part of the gradient. It is suggested that leaf habit plays an important role in determining the function of species and their response to the climatic gradient.