Università degli Studi di Padova, Department Territorio e Sistemi Agro-Forestali, Legnaro (PD), Italy.
New Phytol. 2011 Jan;189(1):241-52. doi: 10.1111/j.1469-8137.2010.03455.x. Epub 2010 Sep 14.
• Low temperatures limit the fixation of photosynthates and xylogenesis. Here, we hypothesized that reduced longitudinal growth in trees at high altitude is related to the lower hydraulic efficiency of the transport system. • Apical buds of Norway spruce (Picea abies) trees at high and low elevation were heated during 2006 and 2007. At the end of the experiment, trees were felled. Longitudinal increments and tracheid lumen areas were measured along the stem. Apical hydraulic conductivity (k) was estimated from anatomical data. • Before heating, high-altitude trees showed fewer (P = 0.002) and smaller (P = 0.008) apical conduits, and therefore reduced k (P = 0.016) and stem elongation (P < 0.0001), in comparison with trees at low elevation. After 2 yr of heating, k increased at both high (P = 0.014) and low (P = 0.047) elevation. Only high-altitude trees showed increased stem elongation, which reached the same magnitude as that of controls at low elevation (P = 0.735). Heating around the apical shoots did not appear to induce significant changes in conduit dimension along the rest of the stem. • The total number and size of xylem elements at the stem apex are strongly constrained by low temperatures. Trees at high altitude are therefore prevented from building up an efficient transport system, and their reduced longitudinal growth reflects strong hydraulic limitations.
• 低温限制了光合作用产物和木质部形成的固定。在这里，我们假设高海拔地区树木的纵向生长减少与运输系统的水力效率较低有关。• 在 2006 年和 2007 年，对高海拔和低海拔挪威云杉（Picea abies）树的顶芽进行了加热。实验结束时，将树木砍伐。沿着树干测量纵向增量和管胞腔面积。根据解剖学数据估算顶端水力传导度（k）。• 在加热之前，与低海拔地区的树木相比，高海拔地区的树木具有较少的（P = 0.002）和较小的（P = 0.008）顶导管，因此 k（P = 0.016）和茎伸长率（P < 0.0001）降低。经过 2 年的加热，高海拔（P = 0.014）和低海拔（P = 0.047）的 k 均增加。只有高海拔的树木表现出茎伸长的增加，其增加幅度与低海拔地区的对照相同（P = 0.735）。围绕顶芽的加热似乎并没有引起沿树干其余部分导管尺寸的显著变化。• 茎尖木质部元素的总数和大小受到低温的强烈限制。因此，高海拔地区的树木无法建立有效的运输系统，其纵向生长的减少反映了强烈的水力限制。
