Comparison of Leaf Traits and Branching Patterns between Acacia tortilis (Forsk.) Hayne subsp. raddiana (Savi) Brenan, Balanites aegyptiaca (L.) Del. and Ziziphus mauritiana Lam. Seedlings Originated from the Sahel

Aims: The aim of this study was to compare the leaf traits and branching patterns between Acacia tortilis, Balanites aegyptiaca and Ziziphus mauritiana seedlings, three species occurring in the same range in the Sahel, a semi-arid tropical area of Africa. Study Design: Seeds used in this experiment were collected from a semi-arid area (16°20’N, 15°25’W), from species growing in their natural range in the Sahel. Seeds were after transferred at the experimental site where they were germinated and grown in a common garden experiment, on an area of 1300 m². Place and Duration of Study: The experimental site was located at around 400 km south of the seed origin (17°33'N, 14°55'W). The experiments were carried out between October 2002 and October 2004. Methodology: The seedlings were watered three days a week from the beginning of the experiment until July 2004. Thereafter, seedlings were assessed at 11 months, 16 months old, and at 24 months after the seed germination date. In the assessment, we measured the length (LGU) and the number (NGU) of growth units, the number of nodes (Nnode), and leaves (Nleaf), and the single (Aleaf) and total (Afoliage) leaf areas. Results: Following the water stress, Nleaf and Aleaf only decreased in A. tortilis, to tightly control the transpiration. Aleaf increased in B. aegyptiaca and Z. mauritiana, due to persistent leaves flushed before the water stress. Afoliage, NGU and Nnode were generally consistent, while LGU decreased in B. aegyptiaca. The defoliation in dry season despite the watering suggested an endogen control, allowing the species to escape harsh conditions in their natural range. Conclusion: The study do not support the hypothesis according to which species naturally coexisting are likely to display similar trend in leaf traits and branching patterns in response to drought. The study has been limited to three weeks of water stress and deserves to be extending to provide more insight into traits pattern for a longer period of water stress.