Research Highlights: Our results provide novel perspectives on the effectiveness and collapse of compensatory mechanisms of tracheid development of Norway spruce during intra-seasonal drought and the environmental control of intra-annual density fluctuations. Background and Objectives: This study aimed to compare and integrate complementary methods for investigating intra-annual wood formation dynamics to gain a better understanding of the endogenous and environmental control of tree-ring development and the impact of anticipated climatic changes on forest growth and productivity. Materials and Methods: We performed an integrated analysis of xylogenesis observations, quantitative wood anatomy, and point-dendrometer measurements of Norway spruce (Picea abies (L.) Karst.) trees growing along an elevational gradient in South-western Germany during a growing season with an anomalous dry June followed by an extraordinary humid July. Results: Strong endogenous control of tree-ring formation was suggested at the highest elevation where the decreasing rates of tracheid enlargement and wall thickening during drought were effectively compensated by increased cell differentiation duration. A shift to environmental control of tree-ring formation during drought was indicated at the lowest elevation, where we detected absence of compensatory mechanisms, eventually stimulating the formation of an intra-annual density fluctuation. Transient drought stress in June also led to bimodal patterns and decreasing daily rates of stem radial displacement, radial xylem growth, and woody biomass production. Comparing xylogenesis data with dendrometer measurements showed ambivalent results and it appears that, with decreasing daily rates of radial xylem growth, the signal-to-noise ratio in dendrometer time series between growth and fluctuations of tree water status becomes increasingly detrimental. Conclusions: Our study provides new perspectives into the complex interplay between rates and durations of tracheid development during dry-wet cycles, and, thereby, contributes to an improved and mechanistic understanding of the environmental control of wood formation processes, leading to the formation of intra-annual density fluctuations in tree-rings of Norway spruce.

中文翻译：

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季节内干旱对挪威云杉沿梯度上升的气管分化动力学和季节性生长动力学的影响

研究重点：我们的结果为季节内干旱期间挪威云杉的气管发育补偿机制的有效性和崩溃以及年内密度波动的环境控制提供了新颖的观点。背景与目的：本研究旨在比较和整合调查年内木材形成动态的补充方法，以更好地了解树木年轮发展的内生和环境控制以及预期的气候变化对森林生长和生产力的影响。材料和方法：我们对挪威云杉（云杉（Picea abies）（L.）喀斯特（Karst）。树木在德国西南部的海拔梯度上生长，生长季节异常干燥的6月，接着是异常潮湿的7月。结果：建议在最高海拔高度对树轮形成进行强力的内源性控制，干旱期间气管扩张和壁增厚的减少速率可以通过增加细胞分化持续时间来有效补偿。在最低海拔表明干旱期间已转向环境控制的年轮形成，在那里我们检测到没有补偿机制，最终刺激了年内密度波动的形成。6月的短暂干旱胁迫也导致了双峰模式，并降低了茎径向位移，径向木质部生长和木质生物量生产的日速率。将木屑生成数据与树木密度计的测量结果进行比较显示出矛盾的结果，并且似乎随着daily木木质部日生长速率的降低，结论：我们的研究为干湿循环中气管发育速率和持续时间之间的复杂相互作用提供了新的观点，从而有助于对木材形成过程的环境控制的改进和机械理解，从而导致木材内部形成。 -挪威云杉的年轮密度波动。