Surface Reduction and its Significance as a Hydroecological Factor

Abstract

Most of the perennial desert plants of Israel are seasonally dimorphic. Their larger winter leaves fall off in early summer and are replaced by small summer leaves. This leaf change causes a marked reduction in the transpiring mass and is much more important as a hydro-ecological factor than the seasonal decrease in transpiration rate. Transpiration measurements made on the same day have shown no marked differences between winter and summer leaves. On the other hand the reduction in the dry weight of the transpiring body during the summer was found to be 84.5%, 76% and 62.8% for Poterium spinosum, Artemisia monosperma and Helianthemum ellipticum, respectively, while the reduction in fresh weight of Zygophyllium dumosum averaged 87.4%. The rate and extent of the reduction of the transpiring body may change even for the same species. It is determined by the available water which in turn depends on the rainfall, the depth of the soil layers, the age of the plants, its roots dimensions, as well as many other factors.