Research linking soil moisture availability to nonstructural carbohydrate (NSC) storage suggests greater NSC reserves promote survival under acute water stress, but little is known about how NSC allocation responds to long-term differences in water availabilty. We hypothesized populations experiencing chronic or frequent water stress shift carbon allocation to build greater NSC reserves for increased survival probability during drought relative to populations rarely experiencing water stress. Over a year, we measured soluble sugar and starch concentrations from branches, stems, and coarse roots of mature Pinus palustris trees at two sites differing in long-term soil moisture availability. Xeric and mesic populations exhibited a cycle of summer depletion-winter accumulation in root starch. Xeric populations reached a maximum root starch concentration approximately 1–2 months later than mesic populations, indicating delayed summer depletion. Xeric and mesic populations reached the same minimum root starch at similar times, suggesting extended winter accumulation for xeric populations. These results suggest seasonal mobilization from root starch is compressed into a shorter interval for xeric populations instead of consistently greater reserves as hypothesized. Seasonal trends differed little between xeric and mesic populations for starch and sugars, suggesting the importance of roots in seasonal carbon dynamics and the primacy of starch for storage. If roots are the primary organ for longterm storage, then our results suggest that whole-plant mobilization and allocation respond to chronic differences in water availability.

中文翻译：

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相对于良性对应物，干燥树种群的根淀粉表现出延迟的夏季枯竭

将土壤水分的可利用性与非结构性碳水化合物（NSC）储存联系起来的研究表明，更大的NSC储备可促进急性水分胁迫下的生存，但人们对NSC的分配如何响应长期的水分利用能力差异知之甚少。我们假设经历长期或频繁的水分胁迫转移碳分配的种群相对于很少遭受水分胁迫的种群建立更大的NSC储备，以增加干旱期间的生存概率。一年多的时间，我们测量了成熟松松枝，茎和粗根中的可溶性糖和淀粉浓度长期土壤水分可利用性不同的两个地点的树木。旱生和中生种群在根淀粉中表现出夏季枯竭-冬季积累的循环。干旱人群的最高根淀粉浓度比中等人群晚了1-2个月，这表明夏季枯竭有所延迟。旱生和中生种群在相似的时间达到相同的最小根淀粉，这表明旱生种群的冬季积累时间延长。这些结果表明，针对干性种群，根淀粉的季节性动员被压缩为较短的间隔，而不是假设的那样始终具有更大的储备。干燥和中生人群中淀粉和糖的季节性趋势差异不大，这表明根在季节性碳动态中的重要性和淀粉在储存中的首要性。