The present study analyses plant diversity and evaluates the relationship between edaphic variables and the distribution and grouping of plant species in the Aswan Reservoir area, South Egypt. The dominant families were Fabaceae, Poaceae, and Asteraceae, forming 38.82% of the total flora recorded. The main bulk of the flora recorded (50.59%) belonged to the cosmopolitan, neotropical, pantropical, and palaeotropical chorotypes. A TWINSPAN analysis produced 10 vegetation clusters. Inundation levels showed a high correlation with species richness. The seasonally inundated area in Bute El-Hasaya and Maezana Belal (cluster V) had the highest species richness (36.50), while the lowest species richness (4.50) was in the shoreline of Philae, Awad, and Heisa islands (cluster IX). The DCA ordination depicted the environmental gradient expressed by the cluster analysis, and the resulting vegetation groups represented a distinct microhabitat. The CCA ordination indicates that the separation of vegetation group (A) along the axis was affected by the concentration of K, Mg, and CO3, and the vegetation group (B) was significantly associated with the total dissolved salts and the concentration of Cl. Moreover, the vegetation group (C) correlated significantly with pH, electrical conductivity, organic matter content, and SO3, HCO3, PO4, Na, and Ca concentrations.

The present study was undertaken to survey the floristic composition in the islands and shorelines in Aswan Reservoir, south of the River Nile at Aswan Governorate, Egypt. Four elements of vegetation were analyzed: floristic composition, lifespan, life form, and phytogeographical affinities. A total of 165 species were recorded belonging to 134 genera in 45 families of vascular plants, of which six species were new to the flora of Aswan and Nubia (Amaranthus spinosus, Doellia bovei, Eleocharis parvula, Haematoxylum campechianum, Polygonum aviculare, and Pithecellobium dulce). The most represented families are Leguminosae, Poaceae, and Compositae. Species richness is highest in low-lying areas (shorelines) liable to flooding, compared to those of the islands in the river. The recorded flora consists of 50.91% perennials and 49.09% annuals. Therophytes and phanerophytes were the predominant life forms. Phytogeographical analysis revealed the prevalence of the pantropical (28.48%), palaeotropical (17.57%), and cosmopolitan (16.36%) plant species. Monoregional chorotype was represented by 29 species (17.58%) of the recorded flora with the Sudano-Zambezian species (11.52%) being the highest chorotype, while pure Mediterranean species were very poorly represented (3.63%). Biregional chorotype was represented by 25 species (15.15%), while the pluriregional chorotype was accounted for 2.43% of recorded species.

T HE PRESENT investigation involves the studies of physiological responses of A. raddiana (savi) Brenan and A. nilotica (L.) seedlings under extreme arid conditions. Experiments were performed in a hyper arid environment to study the effects of drought stress using different water regimes at 12%, 9%, 6%, 4% and 2%. Photosynthesis and transpiration rate were measured under full Photosynthetic Active Radiationrange (0-2500μmols -1 m -2 ) and instantaneous water use efficiency was calculated.A. raddiana and A. nilotica showed maximum photosynthesis rate under 4% and 12% soil moisture content, respectively at high Photosynthetic Active Radiation levels, maximum transpiration rate of A. raddiana recorded at 4% soil moisture content and at 9% soil moisture content in A. nilotica at highest Photosynthetic Active Radiation. The maximum instantaneous water use efficiency was noticed in A. raddiana at 12% soil moisture content, while A. nilotica showed maximum instantaneous water use efficiency at 6% soil moisture content at high Photosynthetic Active Radiation level.A. raddiana acted as water spender ideal desert plant at high Photosynthetic Active Radiation. Other wise A. nilotica maximised photosynthesis rate and minimised transpiration rate giving maximum instantaneous water use efficiency at high Photosynthetic Active Radiation and low soil moisture content levels.

The present investigation involves the studies of water use efficiency of Acacia seyal (Del.) seedlings under extreme arid conditions. Experiments were performed in a hyper arid environment to study the effects of drought stress using different water regimes at 12%, 9%, 6%, 4% and 2%. Calculated instantaneous water use efficiency was measured under full Photosynthetic Active Radiation range (0-2500μmols-1 m-2). Acacia seyal showed maximum photosynthesis rate at 9% soil moisture content, and at high Photosynthetic Active Radiation levels. Maximum transpiration rate recorded at 9% soil moisture content at highest Photosynthetic Active Radiation. The maximum instantaneous water use efficiency was noticed at 4% soil moisture content at high Photosynthetic Active Radiation level. Acacia seyal maximized photosynthesis rate and minimized transpiration rate, giving maximum instantaneous water use efficiency at the high Photosynthetic Active Radiation and low soil moisture content levels.