| Popis: |
Transpirational water loss of Scaevola plumieri (L) Vahl. (= Scaevola thunbergii Eckl. & Zeyh.) (Goodeniaceae), a dune pioneer plant along the eastern and southern coasts of South Africa, was measured over a wide range of atmospheric conditions and related to the atmospheric vapour pressure deficit (VPD). A plot of leaf transpiration rate (E) against VPD yielded a curvilinear relationship (r[sup 2] = 0.88, P = 0.000). As both leaf and canopy E were found to be closely coupled to atmospheric conditions, this correlation was used to calculate canopy E for entire days. The bulk volumes of water transpired per day were related to the mean daily temperature as recorded at a nearby weather station and were strongly related (r2 = 0.71, P = 0.0037). This correlation allowed the bulk volume of water transpired by one square metre of a S. plumieri-covered dune to be calculated on a daily basis for an entire year. Transpirational losses (566 litres) in 1997 were then compared with rainfall (539 litres), indicating that rainfall was perhaps insufficient to support the plants that year. Similar deficits were calculated for 1996, suggesting that plants were possibly reliant on water stored in the sand or taped ground water. This species showed an unusual positive response of increasing leaf conductance to increasing VPD over the range 0-3 kPa. |
