Département des Sciences Fondamentales, Université du Québec à Chicoutimi, Chicoutimi (QC), Canada.
Ann Bot. 2013 Dec;112(9):1911-20. doi: 10.1093/aob/mct243. Epub 2013 Nov 7.
Ongoing global warming has been implicated in shifting phenological patterns such as the timing and duration of the growing season across a wide variety of ecosystems. Linear models are routinely used to extrapolate these observed shifts in phenology into the future and to estimate changes in associated ecosystem properties such as net primary productivity. Yet, in nature, linear relationships may be special cases. Biological processes frequently follow more complex, non-linear patterns according to limiting factors that generate shifts and discontinuities, or contain thresholds beyond which responses change abruptly. This study investigates to what extent cambium phenology is associated with xylem growth and differentiation across conifer species of the northern hemisphere.
Xylem cell production is compared with the periods of cambial activity and cell differentiation assessed on a weekly time scale on histological sections of cambium and wood tissue collected from the stems of nine species in Canada and Europe over 1-9 years per site from 1998 to 2011.
The dynamics of xylogenesis were surprisingly homogeneous among conifer species, although dispersions from the average were obviously observed. Within the range analysed, the relationships between the phenological timings were linear, with several slopes showing values close to or not statistically different from 1. The relationships between the phenological timings and cell production were distinctly non-linear, and involved an exponential pattern.
The trees adjust their phenological timings according to linear patterns. Thus, shifts of one phenological phase are associated with synchronous and comparable shifts of the successive phases. However, small increases in the duration of xylogenesis could correspond to a substantial increase in cell production. The findings suggest that the length of the growing season and the resulting amount of growth could respond differently to changes in environmental conditions.
全球变暖仍在持续，这可能导致各种生态系统的物候模式发生变化，例如生长季的开始时间和持续时间。线性模型通常被用来推断这些物候变化，并预测相关生态系统特性（如净初级生产力）的变化。然而，在自然界中，线性关系可能只是特殊情况。根据产生变化和不连续的限制因素，或者包含超过其之后响应会突然变化的阈值，生物过程通常遵循更复杂的非线性模式。本研究调查了在北半球的针叶树种中，形成层物候与木质部生长和分化之间的关联程度。
在 1998 年至 2011 年期间，在加拿大和欧洲的 9 个地点，每年每个地点采集 1 到 9 年的茎干组织的形成层和木质部组织的切片，在每周的时间尺度上比较木质部细胞的产生与形成层活动和细胞分化的时期。
尽管在平均值上存在明显的分散，但在针叶树种中，木质部发生的动态非常相似。在所分析的范围内，物候定时之间的关系是线性的，几个斜率值接近或统计学上与 1 没有差异。物候定时与细胞产生之间的关系明显是非线性的，涉及指数模式。
树木根据线性模式调整其物候定时。因此，一个物候期的变化与后续阶段的同步和可比变化相关联。然而，木质部发生时间的微小延长可能对应于细胞产生的大量增加。研究结果表明，生长季的长度和由此产生的生长量可能会对环境条件的变化产生不同的响应。
