Veenendaal Elmar M, Mantlana Khanyisa B, Pammenter Norman W, Weber Piet, Huntsman-Mapila Phillipa, Lloyd Jon
Harry Oppenheimer Okavango Research Centre, University of Botswana, Private Bag 285, Maun, Botswana.
Tree Physiol. 2008 Mar;28(3):417-24. doi: 10.1093/treephys/28.3.417.
We investigated differences in physiological and morphological traits between the tall and short forms of mopane (Colophospermum mopane (Kirk ex Benth.) Kirk ex J. Léonard) trees growing near Maun, Botswana on a Kalahari sandveld overlying an impermeable calcrete duricrust. We sought to determine if differences between the two physiognomic types are attributable to the way they exploit available soil water. The tall form, which was located on deeper soil than the short form (5.5 versus 1.6 m), had a lower leaf:fine root biomass ratio (1:20 versus 1:6), but a similar leaf area index (0.9-1.0). Leaf nitrogen concentrations varied between 18 and 27 mg g(-1) and were about 20% higher in the tall form than in the short form. Maximum net assimilation rates (A sat) occurred during the rainy seasons (March-April 2000 and January-February 2001) and were similar in the tall and short forms (15-22 micromol m(-2) s(-1)) before declining to less than 10 micromol m(-2) s(-1) at the end of the rainy season in late April. As the dry season progressed, A sat, soil water content, predawn leaf water potential (Psi pd) and leaf nitrogen concentration declined rapidly. Before leaf abscission, Psi pd was more negative in the short form (-3.4 MPa) than in the tall form (-2.7 MPa) despite the greater availability of soil water beneath the short form trees. This difference appeared attributable to differences in root depth and density between the physiognomic types. Stomatal regulation of water use and carbon assimilation differed between years, with the tall form having a consistently more conservative water-use strategy as the dry season progressed than the short form.
我们研究了生长在博茨瓦纳马翁附近卡拉哈里沙地、不透水钙质硬壳之上的两种形态的猴面包树（Colophospermum mopane (Kirk ex Benth.) Kirk ex J. Léonard），即高大形态和矮小形态之间生理和形态特征的差异。我们试图确定这两种形态类型之间的差异是否归因于它们利用土壤有效水分的方式。高大形态的树生长在比矮小形态更深的土壤中（分别为5.5米和1.6米），其叶与细根生物量比更低（1:20对比1:6），但叶面积指数相似（0.9 - 1.0）。叶片氮浓度在18至27毫克/克之间，高大形态比矮小形态高约20%。最大净同化率（A sat）出现在雨季（2000年3月 - 4月和2001年1月 - 2月），高大形态和矮小形态的最大净同化率相似（15 - 22微摩尔·平方米⁻²·秒⁻¹），之后在4月末雨季结束时降至低于10微摩尔·平方米⁻²·秒⁻¹。随着旱季推进，A sat、土壤含水量、黎明前叶水势（Ψ pd）和叶片氮浓度迅速下降。在落叶前，尽管矮小形态树木下方土壤水分更充足，但矮小形态的Ψ pd（-3.4兆帕）比高大形态（-2.7兆帕）更负。这种差异似乎归因于这两种形态类型在根深度和密度上的差异。不同年份气孔对水分利用和碳同化的调节不同，随着旱季推进，高大形态的水分利用策略始终比矮小形态更保守。
