Department of Botany, University of Innsbruck, Innsbruck, Austria.
Oecologia. 2010 Oct;164(2):321-30. doi: 10.1007/s00442-010-1648-7. Epub 2010 May 9.
In the European Alps, Rhododendron ferrugineum grows in silicate regions while Rhododendron hirsutum is restricted to limestone areas. At geologically mixed sites, also hybrids (Rhododendron × intermedium) can occur. We hypothesised that hydraulic properties would vary with the species' habitat requirements. Key hydraulic parameters (vulnerability to drought-induced embolism, stomata regulation) and related wood characteristics as well as diurnal courses of water potential (Ψ) and stomatal conductance were analysed on plants growing on a silicate, a limestone and a geologically mixed site. Highest embolism resistance[Ψ at 50% loss of conductivity (Ψ (50)), -3.24 ± 0.18 MPa] and the highest safety margin between the Ψ at stomata closure (Ψ (SC) at 10% of maximal leaf conductance) and Ψ (50) were observed in R. hirsutum at the limestone site (1.57 MPa). Like in R. ferrugineum, hydraulic parameters indicated less resistance at the geologically mixed site. Highest Ψ (50) (-1.95 ± 0.12 MPa), corresponding to wide conduits and a reduced conduit wall reinforcement, was found in R. × intermedium. Diurnal courses indicated a rapid stomata closure in response to low Ψ in R. hirsutum and R. × intermedium. The plasticity in drought adaptation of R. hirsutum corresponds to its ability to colonise dry limestone areas. In contrast, hydraulic limitations of R. × intermedium may explain restrictions to rather moist sites. This study provides insight into the role of xylem hydraulics and stomata regulation in shrub water relations, interspecific and site-specific differences in drought adaptation, as well as effects of hybridisation on plant hydraulics.
在欧洲阿尔卑斯山，长叶杜鹃生长在硅酸盐地区，而密枝杜鹃则局限于石灰岩地区。在地质混合的地点，也会出现杂种（Rhododendron × intermedium）。我们假设水力特性会随物种的栖息地需求而变化。关键水力参数（对干旱引起的栓塞的脆弱性、气孔调节）和相关的木材特性以及水势（Ψ）和气孔导度的日进程，在生长在硅酸盐、石灰岩和地质混合地点的植物上进行了分析。在石灰岩地点，密枝杜鹃具有最高的栓塞抗性[Ψ 在 50%导性丧失时（Ψ（50）），-3.24 ± 0.18 MPa]和气孔关闭时的 Ψ（SC）与 Ψ（50）之间的最大安全裕度（1.57 MPa）。与长叶杜鹃相似，水力参数表明地质混合地点的阻力较小。在 Rhododendron × intermedium 中，最高的 Ψ（50）（-1.95 ± 0.12 MPa），对应于宽导管和减少的导管壁加固。日进程表明，在 Rhododendron hirsutum 和 Rhododendron × intermedium 中，气孔会迅速关闭以响应低 Ψ。密枝杜鹃对干旱的适应能力强，可塑性大，因此能够适应干燥的石灰岩地区。相比之下，Rhododendron × intermedium 的水力限制可能解释了其对较湿润地点的限制。本研究深入了解了木质部水力和气孔调节在灌木水分关系中的作用、种间和地点间干旱适应的差异，以及杂交对植物水力的影响。
