Key message

Variability in xylem and phloem phenology among years and species is caused by contrasting temperatures prevailing at the start of the growing season and species-specific sensitivity to drought.

Abstract

The focus of this study was to determine temporal dynamics of xylem and phloem formation in co-occurring deciduous and evergreen coniferous species in a dry inner Alpine environment (750 m a.s.l., Tyrol, Austria). By repeated micro-sampling of the stem, timing of key phenological dates of xylem and phloem formation was compared among mature Pinus sylvestris, Larix decidua and Picea abies during two consecutive years. Xylem formation in P. sylvestris started in mid and late April 2011 and 2012, respectively, and in both years about 2 week later in P. abies and L. decidua. Phloem formation preceded xylem formation on average by 3 week in P. sylvestris, and c. 5 week in P. abies and L. decidua. Based on modeled cell number increase, tracheid production peaked between early through late May 2011 and late May through mid-June 2012. Phloem formation culminated between late April and mid-May in 2011 and in late May 2012. Production of xylem and phloem cells continued for about 4 and 5–6 months, respectively. High variability in xylem increment among years and species is related to exogenous control by climatic factors and species-specific sensitivity to drought, respectively. On the other hand, production of phloem cells was quite homogenous and showed asymptotic decrease with respect to xylem cells indicating endogenous control. Results indicate that onset and culmination of xylem and phloem formation are controlled by early spring temperature, whereby strikingly advanced production of phloem compared to xylem cells suggests lower temperature requirement for initiation of the former.

中文翻译：

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暴露于干旱的共生针叶树的木质部和韧皮部物候。

 关键信息

木质部和韧皮部物候学在年份和物种之间的变异是由生长季节开始时的不同温度和物种对干旱的特定敏感性引起的。

 抽象的

本研究的重点是确定干燥的内高山环境（奥地利蒂罗尔州 750 m asl）中同时存在的落叶和常绿针叶树种的木质部和韧皮部形成的时间动态。通过对茎进行重复微采样，连续两年比较了成熟樟子松、落叶松和冷杉木质部和韧皮部形成的关键物候日期的时间。 P. sylvestris的木质部形成分别于 2011 年 4 月中下旬和 2012 年 4 月下旬开始，而在这两年中， P. abies和L. decidua 的木质部形成均晚于约两周。在P. sylvestris中，韧皮部形成比木质部形成平均早 3 周，并且c ．在P. abies和L. decidua中生长 5 周。根据模拟的细胞数量增加，管胞产量在 2011 年 5 月上旬至下旬和 5 月下旬至 2012 年 6 月中旬之间达到峰值。韧皮部形成在 2011 年 4 月下旬至 5 月中旬和 2012 年 5 月下旬之间达到顶峰。木质部和韧皮部细胞的生产继续进行分别持续约 4 个月和 5-6 个月。木质部增量在年份和物种之间的高度变异性分别与气候因素的外源控制和物种对干旱的特异性敏感性有关。另一方面，韧皮部细胞的产生非常均匀，并且相对于木质部细胞显示渐近减少，表明内源控制。结果表明，木质部和韧皮部形成的开始和高潮受早春温度控制，因此与木质部细胞相比，韧皮部的产生显着提前，表明前者的起始温度要求较低。