Leaf anatomy and its relation to the ecophysiology of some non-succulent desert plants from Egypt

A quantitative study of leaf anatomy of 20 species of some non-succulent perennial desert plants belonging to 12 families of the Dicotyledoneae is provided. The species were collected from natural desert habitats belonging to three phytogeographical regions of Egypt. Features representing xeromorphy include small leaf or leaflet area (18 species), pubescent surfaces (16 species), amphistomaticy, iso-bilateral leaf construction and multilayered palisade of two to four layers (18 species). Particular attention is given to quantify the palisade properties as well as the hydraulic conductance (Kh) of the xylem tissue supplying the transpiring areas. The ratio of the palisade cell surface area/the leaf or leaflet area (Apal/A) ranges from 22•6 inAstragalus spinosusto 49•6 inZilla spinosa. Moreover,Apal/Ais highly correlated with the palisade thickness (r= 0•541,N= 100,p= 0•0001) and with the thickness of lamina. The predictedKhof the xylem is calculated from the conduit lumen diameters using the Hagen-Poiseuille relation. Eighteen species show low predictedKhvalues ranging from 0•6 to 300•5 × 10−13m4MPa−1s−1. The highest values of predictedKhoccur inGomphocarpus sinaicusandChrozophora obliqua, which have the highest leaf areas. PredictedKhcorrelates very well with leaf or leaflet area supplied by the petiole or petiolule (r= 0•685,N= 100,p= 0•0001). The efficiency of xylem conductance is further identified by calculations of the leaf specific conductance (LSC=Kh/distal leaf or leaflet area) and the predicted maximum pressure gradients (MPa m−1). The measured anatomical parameters and their correlations are discussed in terms of the ecophysiological adjustments of the desert plants to their habitat.