Institute of Botany, Leopold-Franzens-University of Innsbruck, Sternwartestrasse 15, A-6020 Innsbruck, Austria.
Tree Physiol. 2010 Apr;30(4):490-501. doi: 10.1093/treephys/tpq003. Epub 2010 Mar 1.
We determined the temporal dynamics of cambial activity and xylem cell differentiation of Scots pine (Pinus sylvestris L.) within a dry inner Alpine valley (750 m a.s.l., Tyrol, Austria), where radial growth is strongly limited by drought in spring. Repeated micro-sampling of the developing tree ring of mature trees was carried out during two contrasting years at two study plots that differ in soil water availability (xeric and dry-mesic sites). In 2007, when air temperature at the beginning of the growing season in April exceeded the long-term mean by 6.4 degrees C, cambial cell division started in early April at both study plots. A delayed onset of cambial activity of c. 2 weeks was found in 2008, when average climate conditions prevailed in spring, indicating that resumption of cambial cell division after winter dormancy is temperature controlled. Cambial cell division consistently ended about the end of June/early July in both study years. Radial enlargement of tracheids started almost 3 weeks earlier in 2007 compared with 2008 at both study plots. At the xeric site, the maximum rate of tracheid production in 2007 and 2008 was reached in early and mid-May, respectively, and c. 2 weeks later at the dry-mesic site. Since in both study years more favorable growing conditions (i.e., an increase in soil water content) were recorded during summer, we suggest a strong sink competition for carbohydrates to mycorrhizal root and shoot growth. Wood formation stopped c. 4 weeks earlier at the xeric compared with the dry-mesic site in both years, indicating a strong influence of drought stress on cell differentiation. This is supported by radial widths of earlywood cells, which were found to be significantly narrower at the xeric than at the dry-mesic site (P < 0.05). Repeated cellular analyses during the two growing seasons revealed that, although spatial variability in the dynamics and duration of cell differentiation processes in P. sylvestris exposed to drought is strongly influenced by water availability, the onset of cambial activity and cell differentiation is controlled by temperature.
我们在一个干旱的阿尔卑斯山内部山谷（海拔 750 米，奥地利蒂罗尔州）内确定了苏格兰松（Pinus sylvestris L.）形成层活动和木质部细胞分化的时间动态，在那里，春季干旱强烈限制了径向生长。在两个不同的研究点（干旱和干燥-湿润点），在两个对比年份中对成熟树木的发育年轮进行了重复的微采样，这些研究点的土壤水分供应不同。在 2007 年，4 月初的空气温度比长期平均值高出 6.4°C，两个研究点的形成层细胞分裂都在 4 月初开始。在 2008 年，当春季平均气候条件占主导地位时，发现形成层活动的开始延迟了大约 2 周，这表明休眠后形成层细胞分裂的恢复受温度控制。在这两个研究年份中，形成层细胞分裂始终在 6 月底/7 月初左右结束。在 2007 年，与 2008 年相比，两个研究点的管胞径向扩大开始得早了近 3 周。在干旱点，2007 年和 2008 年的最大管胞产生速率分别在 5 月初和中旬达到，而在湿润点则晚了大约 2 周。由于在这两个研究年份中，夏季记录到了更有利的生长条件（即土壤水分含量增加），我们建议碳水化合物的强烈汇竞争是根和茎的菌根生长。在这两年中，在干旱点，木质部的形成比在湿润点早停止了约 4 周，这表明干旱胁迫对细胞分化有强烈影响。这得到了早材细胞径向宽度的支持，发现干旱点的早材细胞比湿润点的明显更窄（P < 0.05）。在两个生长季节进行的重复细胞分析表明，尽管暴露于干旱条件下的苏格兰松细胞分化过程的动态和持续时间的空间变异性受到水分供应的强烈影响，但形成层活动和细胞分化的开始受温度控制。
