Eco-physiological studies on desert plants : VIII. Root penetration of Leptadenia pyrotechnica (Forsk.) Decne. in relation to its water balance.

1. Leptadenia pyrotechnica (Forsk.) Decne. is a leafless tree growing under, adverse arid conditions in the valleys of the Eastern Desert in Egypt. 2. The plant cover in areas inhabited by this species is very low and amounts to only 1% in some localities. In such an open vegetation competition between roots is lacking and each root system monopolizes a huge volume of soil. 3. The root system of a small Leptadenia bush penetrates to a depth of 11.5 m and has a lateral extension of 10 m. The root system exploits about 850 m3 of soil. The distribution of the roots and their branching is closely related to the availability of the soil moisture in the different strata. 4. The available soil moisture is not uniform throughout the whole profile. Depending on the average available soil moisture at the different depths, the total available moisture in the soil volume occupied by the root system of Leptadenia bush is found to be about 23000 kg. 5. The annual water output by the studied bush is found to be 5700 kg. This means that the available water in the soil occupied by the root system is sufficient to supply the plant for a period of four years without replenishment by rainfall. 6. The present study shows that the plant can live safely for several years under the severe conditions of the desert. The plant possesses some characteristics which help it to keep its water balance positive through increased absorption.