PREMISE The xylem tissue of plants performs three principal functions: transport of water, support of the plant body, and nutrient storage. Tradeoffs may arise because different structural requirements are associated with different functions or because suites of traits are under selection that relate to resource acquisition, use, and turnover. The structural and functional basis of xylem storage is not well established. We hypothesized that greater starch storage would be associated with greater sapwood parenchyma and reduced fibers, which would compromise resistance to xylem tensions during dehydration. METHODS We measured cavitation resistance, minimum water potential, starch content, and sapwood parenchyma and fiber area in 30 species of southern California chaparral shrubs (evergreen and deciduous). RESULTS We found that species storing greater starch within their xylem tended to avoid dehydration and were less cavitation resistant, and this was supported by phylogenetic independent contrasts. Greater sapwood starch was associated with greater parenchyma area and reduced fiber area. For species without living fibers, the associations with parenchyma were stronger, suggesting that living fibers may expand starch storage capacity while also contributing to the support function of the vascular tissue. Drought-deciduous species were associated with greater dehydration avoidance than evergreens. CONCLUSIONS Evolutionary forces have led to an association between starch storage and dehydration resistance as part of an adaptive suite of traits. We found evidence for a tradeoff between tissue mechanical traits and starch storage; moreover, the evolution of novel strategies, such as starch-storing living fibers, may mitigate the strength of this tradeoff.

中文翻译：

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边材的淀粉贮藏能力与干旱期间避免脱水有关

前提 植物的木质部组织执行三个主要功能：水的运输、植物体的支持和养分储存。权衡可能会出现，因为不同的结构要求与不同的功能相关，或者因为与资源获取、使用和周转相关的一系列特征正在被选择。木质部储存的结构和功能基础尚未建立。我们假设更大的淀粉储存量与更大的边材薄壁组织和减少的纤维有关，这会损害脱水过程中对木质部张力的抵抗力。方法我们测量了 30 种南加州丛林灌木（常绿和落叶）的抗空化能力、最小水势、淀粉含量以及边材薄壁组织和纤维面积。结果我们发现，在木质部内储存更多淀粉的物种倾向于避免脱水并且抗空化能力较差，这得到了系统发育独立对比的支持。较大的边材淀粉与较大的薄壁组织面积和减少的纤维面积有关。对于没有活纤维的物种，与薄壁组织的关联更强，表明活纤维可能会扩大淀粉储存能力，同时也有助于血管组织的支持功能。干旱落叶树种比常绿树种更能避免脱水。结论 进化力量导致淀粉储存和脱水抗性之间存在关联，作为适应性特性的一部分。我们发现了组织力学特性和淀粉储存之间权衡的证据；而且，