Effects of drought stress on the growth of Acacia asak (Forssk.),A. tortilis (Forssk.) and A. gerrardii (Benth) ssp. negevensis (Zoh.)

Abstract

Seedlings of Acacia asak (Forssk.), Acacia tortilis (Forssk.) and Acacia gerrardii (Benth) ssp. negevensis (Zoh.) were produced by seeds collected from trees grown in Asir mountains area at the south-west region of Saudi Arabia. They were watered when depletion of soil water reached either 60% (well-watered) or 90% (water-stressed). The growth of water-stressed acacias was reduced markedly. Total number of leaves and total leaf area decreased by 71 and 77%, respectively and resulted in 80% reduction in leaf dry weight. Stem and total dry weight also reduced whereas root dry weight was not affected. Water-stressed trees allocated relatively more dry weight to the roots at the expense of that allocated to the leaves. A. gerrardii tolerated water stress mainly by decreasing leaf area through leaf shedding and A. tortilis by increasing allocation of dry matter to roots at the expense of leaves whereas A. asak was not affected.