Department of Botany, University of Innsbruck, Sternwartestr. 15, A-6020 Innsbruck, Austria.
Tree Physiol. 2012 Sep;32(9):1161-70. doi: 10.1093/treephys/tps071. Epub 2012 Aug 19.
Leaves, the distal section of the soil-plant-atmosphere continuum, exhibit the lowest water potentials in a plant. In contrast to angiosperm leaves, knowledge of the hydraulic architecture of conifer needles is scant. We investigated the hydraulic efficiency and safety of Pinus pinaster needles, comparing different techniques. The xylem hydraulic conductivity (k(s)) and embolism vulnerability (P(50)) of both needle and stem were measured using the cavitron technique. The conductance and vulnerability of whole needles were measured via rehydration kinetics, and Cryo-SEM and 3D X-ray microtomographic observations were used as reference tools to validate physical measurements. The needle xylem of P. pinaster had lower hydraulic efficiency (k(s) = 2.0 × 10(-4) m(2) MPa(-1) s(-1)) and safety (P(50) = - 1.5 MPa) than stem xylem (k(s) = 7.7 × 10(-4) m(2) MPa(-1) s(-1); P(50) = - 3.6 to - 3.2 MPa). P(50) of whole needles (both extra-vascular and vascular pathways) was - 0.5 MPa, suggesting that non-vascular tissues were more vulnerable than the xylem. During dehydration to - 3.5 MPa, collapse and embolism in xylem tracheids, and gap formation in surrounding tissues were observed. However, a discrepancy in hydraulic and acoustic results appeared compared with visualizations, arguing for greater caution with these techniques when applied to needles. Our results indicate that the most distal parts of the water transport pathway are limiting for hydraulics of P. pinaster. Needle tissues exhibit a low hydraulic efficiency and low hydraulic safety, but may also act to buffer short-term water deficits, thus preventing xylem embolism.
叶片是土壤-植物-大气连续体的最远端部分，其水分势在植物中最低。与被子植物叶片不同，人们对针叶树针叶的水力结构知之甚少。我们研究了辐射松针叶的水力效率和安全性，比较了不同的技术。使用空蚀仪技术测量了针叶和茎的木质部水力传导度（k(s)）和栓塞脆弱性（P(50)）。通过再水合动力学测量了整个针叶的传导度和脆弱性，并使用 Cryo-SEM 和 3D X 射线微断层摄影观察作为参考工具来验证物理测量。辐射松针叶的木质部水力效率（k(s)=2.0×10(-4) m(2) MPa(-1) s(-1)）和安全性（P(50)=-1.5 MPa）低于茎木质部（k(s)=7.7×10(-4) m(2) MPa(-1) s(-1)；P(50)=-3.6 至-3.2 MPa）。整个针叶（血管外和血管途径）的 P(50)为-0.5 MPa，表明非血管组织比木质部更脆弱。在脱水至-3.5 MPa 时，木质部管胞发生崩溃和栓塞，周围组织形成间隙。然而，与可视化结果相比，水力和声学结果存在差异，这表明在将这些技术应用于针叶时需要更加谨慎。我们的结果表明，木质部水运输途径的最远端部分对辐射松的水力性能起限制作用。针叶组织表现出低水力效率和低水力安全性，但也可能起到缓冲短期水分亏缺的作用，从而防止木质部栓塞。
