ADAPTIVE SIGNIFICANCE OF HYGROCHASY AND GROWTH FOR ESTABLISHMENT AND CONSERVATION ECOLOGY OF ANASTATICA HIEROCHUNTICA L. IN EGYPT

Abstract

Hygrochasy is the opening and closing of plant organs enclosing the dispersal units as a function of moisture. Anastatica hierochuntica L. (Brassicaceae) is a lignified desert annual characterized by a highly efficient mechanism of seed dispersal depending on the hygrochastic nature of the dead plant skeletons. The species is widespread in the Egyptian deserts in specified habitat types including water runnels, patches and depression. According to area, depressions are classified into simple and compound. Simple depressions are differentiated into outer and core zones. Compound depressions are differentiated into outer, intermediate and core zones.

Field, laboratory and greenhouse studies were combined to: (1) Detect the anatomical significance of the hygrochastic mechanism of A. hierochuntica; (2) Reveal the spatial pattern interrelationships between A. hierochuntica size-classes in different microhabitats; (3) Investigate the allelopathic potential of the study species on positively and negatively associated species; (4) Explore the flexibility of the morphological and reproductive traits of the species under different simulated rainfall treatments and the possible use of the dry skeleton crown volume as a rain gauge; (5) Study the dynamics of A. hierochuntica populations and to predict life time durations as based on the individual size of the seed bank, under different simulated rainfall treatments.

Unlike the dispersal mechanisms of many desert plants, the whole dead skeleton of A. hierochuntica is involved in seed dispersal and preservation. This process depends on the hygrochastic nature of the lignified conducting tissue that bends when dry and straightens under wet conditions. The anatomical investigation of the hygrochastic mechanism revealed an asymmetric distribution of the cortical and the conducting tissues in the inner and outer sides of the stem of both juvenile and adult plants being greater in the outer side. The lignified conducting tissue of the whole stem controls the movement of the branches.