Sap flow and water use in African baobab (Adansonia digitata L.) seedlings in response to drought stress

The African baobab (Adansonia digitata L.) is an important multi-purpose fruit tree with high potential for domestication in drier Africa. Although adult individuals are well-known to be drought resistant, only little has been reported on how young baobab trees can survive drought Therefore, the aim of this study was to examine shortterm soil drought effects on water relations of baobab seedlings. Baobab seedlings used a limited amount of stored water to buffer daily water deficits (similar to 8.5 g d(-1)), which contributed up to only similar to 17.5% of daily water use and similar to 6% of total plant water. Under drought, a strong reduction in stomatal conductance (similar to 85%) resulted in a midday leaf water potential of -1 MPa and zero stem sap flow followed by significant leaf loss. Plant anatomy evidenced the presence of water storage tissues and the vulnerability to xylem embolism. The taproot was the most important plant part for water storage (68% of total plant water), suggesting root-succulence rather than stem-succulence. When drought intensified, limitation of leaf transpiration and/or root water uptake led to drought-enforced dormancy. Despite the large amounts of water stored in the taproot (similar to 90%) and the stem (similar to 75%), only a limited amount of stored water appeared to be used to sustain upper leaves and plant metabolism during the dormant period, and to facilitate recovery following water supply. Drought avoidance, conservative water use and the presence of internal stored water allow baobab seedlings to survive drought. (C) 2013 SAAB. Published by Elsevier BM. All rights reserved.