Castro-Díez Pilar, Navarro Javier
Departamento de Ecología, Universidad de Alcalá. Ctra. Madrid-Barcelona, km 33.6, E-28871 Alcalá de Henares, Madrid, Spain.
Tree Physiol. 2007 Jul;27(7):1011-8. doi: 10.1093/treephys/27.7.1011.
We compared seedling water relations of three Mediterranean Quercus species (the evergreen shrub Q. coccifera L., the evergreen tree Q. ilex L. subsp. ballota (Desf.) Samp. and the deciduous or marcescent tree Q. faginea L.). We also explored seedling potential for acclimation to contrasting growing conditions. In March, 1-year-old seedlings of the three species were planted in pots and grown outdoors in a factorial combination of two irrigation regimes (daily (HW) and alternate day watering (LW)) and two irradiances (43 and 100% of full sunlight). At the end of July, predawn and midday water potentials (Psi(pd), Psi(md)) were measured, and pressure-volume (P-V) curves were obtained for mature current-year shoots. Species exhibited similar Psi(pd) and Psi(md) values, but differed in leaf morphology and water relations. The evergreens possessed larger leaf mass per area (LMA) and were able to maintain positive turgor pressure at lower water potentials than the deciduous species because of their lower osmotic potential at full turgor. However, the three species had similar relative water contents at the turgor loss point because Q. faginea compensated for its higher osmotic potential with greater cell wall elasticity. Values of Psi(pd) had a mean of -1.12 MPa in LW and -0.63 MPa in HW, and Psi(md) had a mean of -1.13 MPa in full sunlight and -1.64 MPa in shade, where seedlings exhibited lower LMA. However, the P-V curve traits were unaffected by the treatments. Our results suggest that Q. faginea seedlings combine the water-use characteristics of mesic deciduous oak and the drought-tolerance of xeric evergreen oak. The ability of Q. coccifera to colonize drier sites than Q. ilex was not a result of higher drought tolerance, but rather may be associated with other dehydration postponement mechanisms including drought-induced leaf shedding. The lack of treatment effects may reflect a relatively low contrast between treatment regimes, or a low inherent responsiveness of these traits in the study species, or both.
我们比较了三种地中海栎属植物（常绿灌木栓皮栎、常绿乔木冬青栎亚种巴洛塔栎和落叶或半落叶乔木西班牙栓皮栎）的幼苗水分关系。我们还探究了幼苗适应不同生长条件的潜力。3月，将这三个物种的1年生幼苗种植在花盆中，并在两种灌溉方式（每日浇水（HW）和隔日浇水（LW））与两种光照强度（全日照的43%和100%）的析因组合下于户外种植。7月底，测量了黎明前和中午的水势（Ψ(pd)、Ψ(md)），并获取了当年成熟新梢的压力-容积（P-V）曲线。各物种表现出相似的Ψ(pd)和Ψ(md)值，但在叶片形态和水分关系上存在差异。常绿植物的单位面积叶质量（LMA）更大，并且由于其在完全膨压下较低的渗透势，能够在比落叶物种更低的水势下维持正膨压。然而，由于西班牙栓皮栎通过更大的细胞壁弹性补偿了其较高的渗透势，这三个物种在膨压丧失点的相对含水量相似。在LW条件下，Ψ(pd)的平均值为-1.12 MPa，在HW条件下为-0.63 MPa；在全日照下，Ψ(md)的平均值为-1.13 MPa，在遮荫条件下为-1.64 MPa，遮荫条件下幼苗的LMA较低。然而，P-V曲线特征不受处理影响。我们的结果表明，西班牙栓皮栎幼苗兼具中生落叶栎的水分利用特性和旱生常绿栎的耐旱性。与冬青栎相比，栓皮栎能够在更干燥的地点定殖，这并非是其具有更高耐旱性的结果，而是可能与包括干旱诱导落叶在内的其他脱水延迟机制有关。缺乏处理效应可能反映了处理方式之间相对较小的差异，或者这些性状在研究物种中的固有响应性较低，或者两者皆有。
