Key message

Phloem cell production was less influenced by environmental factors than xylem cell production. The moment of maximum number of conducting phloem cells occurred at the end of the growing season.

Abstract

The understanding of the seasonality of phloem production, its dependence on climatic factors and potential trade-offs with xylem cell production is still limited. This study determined key tree-ring phenological events and examined the dynamics of phloem and xylem cell production of Norway Spruce (Picea abies (L.) Karst) by sampling microcores during the growing seasons 2014 and 2015 along an elevational gradient (450 m, 750 m, 1250 m a.s.l.) in south-western Germany. The onset of phloem formation preceded xylem formation at each elevation by approximately 2 weeks, while cessation showed no clear differences between the stands. Maximum rates of xylem and phloem cell production were observed around the summer solstice, independent of elevation. No linear pattern was found in the occurrence of phenological events along the elevational gradient. Phloem formation appeared to be less sensitive to environmental conditions since no difference was found in the number of produced sieve cells between the 2 years of study, whereas the ratio of xylem to phloem cells was significantly smaller in the year 2015 with summer drought. The total number of conducting, non-collapsed phloem cells did not culminate as expected at the time of the potential maximum assimilate production, but at the end of the growing season. Thus, interpretation of phloem formation should not be limited to the function of assimilate transport but should follow a more holistic view of structural–functional relationships of conductive tissues and tree physiological processes.

中文翻译：

---

海拔高度梯度下挪威云杉季节性木质部和韧皮部生产的可塑性

关键信息

韧皮部细胞的产生比木质部细胞的产生受环境因素的影响小。在生长季节结束时，发生了最大数量的韧皮部细胞。

抽象

对韧皮部产生的季节性，其对气候因素的依赖性以及与木质部细胞产生之间的潜在权衡的了解仍然有限。这项研究确定了重要的树木年轮的物候事件，并研究了挪威云杉（Picea abies）韧皮部和木质部细胞产生的动态（L.）Karst）在德国西南部2014和2015年生长季节沿海拔梯度（450 m，750 m，1250 m asl）采样微岩心。韧皮部的形成先于木质部形成，然后在每个海拔升高约2周，而停止则表明林分之间没有明显差异。在夏至前后观察到木质部和韧皮部细胞产生的最大速率，与海拔无关。在沿海拔梯度的物候事件发生中未发现线性模式。韧皮部的形成似乎对环境条件较不敏感，因为在两年的研究中，发现的筛子细胞数量没有差异，而在2015年夏季干旱的情况下，木质部与韧皮部细胞的比例明显较小。总数，未塌陷的韧皮部细胞在潜在的最大同化物产生时未达到预期的高峰，但在生长季节结束时达到了顶点。因此，韧皮部形成的解释不应局限于同化运输的功能，而应遵循传导组织与树木生理过程的结构-功能关系的更全面的观点。