Nonstructural carbohydrates (NSCs) play a critical role in plant physiology and metabolism, yet we know little about their distribution within individual organs such as the stem. This leaves many open questions about whether reserves deep in the stem are metabolically active and available to support functional processes. To gain insight into the availability of reserves, we measured radial patterns of NSCs over the course of a year in the stemwood of temperate trees with contrasting wood anatomy (ring porous vs diffuse porous). In a subset of trees, we estimated the mean age of soluble sugars within and between different organs using the radiocarbon (¹⁴C) bomb spike approach. First, we found that NSC concentrations were the highest and most seasonally dynamic in the outermost stemwood segments for both ring-porous and diffuse-porous trees. However, while the seasonal fluctuation of NSCs was dampened in deeper stemwood segments for ring-porous trees, it remained high for diffuse-porous trees. These NSC dynamics align with differences in the proportion of functional sapwood and the arrangement of vessels between ring-porous and diffuse-porous trees. Second, radial patterns of ¹⁴C in the stemwood showed that sugars became older when moving toward the pith. The same pattern was found in the coarse roots. Finally, when taken together, our results highlight how the radial distribution and age of NSCs relate to wood anatomy and suggest that while deeper, and likely older, reserves in the stemwood fluctuated across the seasons, the deepest reserves at the center of the stem were not used to support tree metabolism under usual environmental conditions.

中文翻译：

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非结构性碳水化合物的季节性波动揭示了温带树木中茎材储备的代谢有效性，与木材的解剖结构相反。

非结构性碳水化合物（NSC）在植物生理和代谢中起着至关重要的作用，但我们对其在茎等单个器官中的分布了解甚少。这就留下了许多悬而未决的问题，即茎深处的储备是否具有代谢活性，是否可用于支持功能性过程。为了深入了解储量的可用性，我们在一年的过程中测量了温带树茎木中NSC的放射状，并与木材的解剖结构形成对比（环状多孔与弥散多孔）。在一部分树木中，我们使用放射性碳估算了不同器官内部和器官之间的可溶性糖的平均年龄（¹⁴C）炸弹秒杀方法。首先，我们发现，无论是环状多孔树还是弥散多孔树，NSC浓度在最外层材中都是最高的，并且是季节性最强的。然而，虽然在深层阔叶木中，环孔树的NSCs的季节性波动得到了抑制，但散孔树的NSC的季节性波动仍然很高。这些NSC动态与功能性边材的比例以及环孔树和弥散孔树之间的血管排列的差异一致。二，放射状花纹¹⁴茎木中的C表明糖向着髓移动时变老了。在粗根中发现了相同的模式。最后，将这些结果综合在一起，我们的结果突出了NSC的径向分布和年龄与木材解剖结构的关系，并表明虽然茎木中的木材储量越深（可能越老）随季节变化，但茎中央的储量最大。在通常的环境条件下不用于支持树木的新陈代谢。