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-succule nt perennial desert plants belonging to 12 families of the Dicotyledon eae is provided. The species were collected from natural desert habita ts belonging to three phytogeographical regions of Egypt. Features rep resenting xeromorphy include small leaf or leaflet area (18 species), pubescent surfaces (16 species), amphistomaticy, iso-bilateral leaf co nstruction and multilayered palisade of two to four layers (18 species ). Particular attention is given to quantify the palisade properties a s well as the hydraulic conductance (Kh) of the xylem tissue supplying the transpiring areas. The ratio of the palisade cell surface area/th e leaf or leaflet area (Apal/A) ranges from 22.6 in Astragalus spinosu s to 49.6 in Zilla spinosa. Moreover, Apal/A is highly correlated with the palisade thickness (r = 0.541, N = 100, p = 0.0001) and with the thickness of lamina. The predicted Kh of the xylem is calculated from the conduit lumen diameters using the Hagen-Poiseuille relation. Eight een species show low predicted Kh values ranging from 0.6 to 300.5 X 1 0(-13) m(4) MPa-1 s(-1). The highest values of predicted Kh occur in G omphocarpus sinaincs and Chrozophora obliqua, which have the highest l eaf areas. Predicted Kh correlates 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 calcula tions of the leaf specific conductance (LSC = Kh/ distal leaf or leafl et area) and the predicted maximum pressure gradients (MPa m(-1)). The measured anatomical parameters and their correlations are discussed i n terms of the ecophysiological adjustments of the desert plants to th eir habitat. (C) 1997 Academic Press Limited.