Finnish Forest Research Institute, Joensuu Research Unit, PO Box 68, FI-80101 Joensuu, Finland.
Tree Physiol. 2012 Aug;32(8):987-97. doi: 10.1093/treephys/tps063.
The timing of bud development in ecodormancy is critical for trees in boreal and temperate regions with seasonally alternating climates. The development of vegetative buds and the growth of primordial shoots (the primordial shoot ratio) in Norway spruce were followed by the naked eye and at stereo and light microscopic levels in fresh-cut and fixed buds obtained by regular field samplings during the spring of 2007, 2008 and 2009. Buds were collected from 15 randomly selected trees (all 16 years old in 2007) of one southern Finnish half-sib family. The air temperature was recorded hourly throughout the observation period. In 2008 and 2009, initial events in the buds, seen as accumulation of lipid droplets in the cortex area, started in mid-March and were depleted in late April, simultaneously with the early development of vascular tissue and primordial needles. In mid-April 2007, however, the development of the buds was at least 10 days ahead as a result of warm spells in March and early April. Variation in the timing of different developmental phases within and among the sample trees was negligible. There was no clear one-to-one correspondence between the externally visible and the internal development of the buds. The dependence of the primordial shoot ratio on different types of temperature sum was studied by means of regression analysis. High coefficients of determination (R(2) ≈ 95%) were attained with several combinations of the starting time (beginning of the year/vernal equinox), the threshold value (from -3 to +5 °C), and the time step (hour/day) used in the temperature summation, i.e., the prediction power of the primordial shoot ratio models turned out to be high, but the parameter estimate values were not unambiguous. According to our results, temperature sums describe the growth of the primordial shoot inside the bud before bud burst. Thus, the results provide a realistic interpretation for the present phenological models of bud development that are based on temperature sums and external observations of bud burst only, and they also provide new tools for improving the models.
在具有季节性交替气候的北方和温带地区，芽发育的时间对于树木至关重要。通过定期野外采样，在 2007 年、2008 年和 2009 年春季获得的新鲜和固定芽中，肉眼和立体及光镜水平观察到挪威云杉营养芽的发育和原始嫩枝（原始嫩枝比例）的生长。芽取自一个南部芬兰半同胞家系的 15 棵随机选择的树木（2007 年全部 16 岁）。在整个观察期间，每小时记录一次空气温度。在 2008 年和 2009 年，芽中可见的初始事件是皮质区脂滴的积累，始于 3 月中旬，4 月下旬耗尽，同时血管组织和原始针叶的早期发育。然而，由于 3 月和 4 月初的温暖天气，2007 年 4 月中旬芽的发育至少提前了 10 天。样本树木内部和之间不同发育阶段的时间变化可以忽略不计。外部可见芽和内部发育之间没有明确的一一对应关系。通过回归分析研究了原始嫩枝比例与不同类型温度总和的关系。使用温度总和的起始时间（年初/春分）、阈值（-3 至+5°C）和时间步长（小时/天）的几种组合，获得了高决定系数（R(2)≈95%），即原始嫩枝比例模型的预测能力很高，但参数估计值并不明确。根据我们的结果，温度总和描述了芽爆裂前芽内原始嫩枝的生长。因此，这些结果为仅基于温度总和和外部芽爆裂观察的芽发育的现有物候模型提供了现实的解释，也为改进模型提供了新的工具。
