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

• Published in: South African journal of botany 2013-09, Vol.88, p.438-446
• Main Authors: Van den Bilcke, N., De Smedt, S., Simbo, D.J., Samson, R.
• Format: Article
• Language: English
• Subjects: Adansonia digitata; adults; Diameter fluctuations; domestication; dormancy; drought; Drought avoidance; drought tolerance; embolism; fruit trees; leaf water potential; leaves; metabolism; Sap flow; seedlings; Semi-arid regions; soil; Stomatal conductance; water flow; Water storage; water stress; water supply; water uptake; xylem
• ISSN: 0254-6299; 1727-9321
• DOI: 10.1016/j.sajb.2013.09.006

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 short-term soil drought effects on water relations of baobab seedlings. Baobab seedlings used a limited amount of stored water to buffer daily water deficits (~8.5gd−1), which contributed up to only ~17.5% of daily water use and ~6% of total plant water. Under drought, a strong reduction in stomatal conductance (~85%) resulted in a midday leaf water potential of −1MPa 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 (~90%) and the stem (~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. •We examined short-term soil drought effects on water relations of baobab seedlings.•Limitation of leaf transpiration and/or root water uptake resulted in drought-enforced dormancy.•Only little plant water was used despite the large amounts of water stored in stem and root.•Drought avoidance, conservative water use and the presence of water storages allowed baobab seedlings to survive drought.