Abstract：
Hydathodes are usually associated with water exudation in plants. However, foliar water uptake (FWU) through the hydathodes has long been suspected in the leaf-succulent genus Crassula (Crassulaceae), a highly diverse group in southern Africa, and, to our knowledge, no empirical observations exist in the literature that unequivocally link FWU to hydathodes in this genus. FWU is expected to be particularly beneficial on the arid western side of southern Africa, where up to 50% of Crassula species occur and where periodically high air humidity leads to fog and/or dew formation. To investigate if hydathode-mediated FWU is operational in different Crassula species, we used the apoplastic fluorescent tracer Lucifer Yellow in combination with different imaging techniques. Our images of dye-treated leaves confirm that hydathode-mediated FWU does indeed occur in Crassula and that it might be widespread across the genus. Hydathodes in Crassula serve as moisture-harvesting structures, besides their more common purpose of guttation, an adaptation that has likely played an important role in the evolutionary history of the genus. Our observations suggest that ability for FWU is independent of geographical distribution and not restricted to arid environments under fog influence, as FWU is also operational in Crassula species from the rather humid eastern side of southern Africa. Our observations point towards no apparent link between FWU ability and overall leaf surface wettability in Crassula. Instead, the hierarchically sculptured leaf surfaces of several Crassula species may facilitate FWU due to hydrophilic leaf surface microdomains, even in seemingly hydrophobic species. Overall, these results confirm the ecophysiological relevance of hydathode-mediated FWU in Crassula and reassert the importance of atmospheric humidity for some arid-adapted plant groups.
摘要：
Hydathodes通常与植物中的水渗出有关。然而,长期以来，人们一直怀疑叶片肉质属Crassula（Crassulaceae）中通过hythodes的叶面水分吸收（FWU），南部非洲的一个高度多样化的群体，and,根据我们的知识，文献中没有经验观察到将FWU与该属的棘突明确联系起来。FWU预计将在南部非洲干旱的西部特别有利，其中高达50％的Crassula物种出现，并且定期高空气湿度导致雾和/或露水形成。为了研究在不同的Crassula物种中是否可以通过线虫介导的FWU进行操作，我们使用了脱体荧光示踪剂LuciferYellow结合不同的成像技术。我们对染料处理过的叶子的图像证实，棘突介导的FWU确实发生在Crassula中，并且可能在整个属中广泛存在。Crassula的Hydathodes用作水分收集结构，除了他们更常见的内脏目的，一种适应可能在该属的进化史中发挥了重要作用。我们的观察表明，FWU的能力与地理分布无关，并且不限于雾影响下的干旱环境，因为FWU也在南部非洲东部相当潮湿的Crassula物种中运作。我们的观察结果表明，在Crassula中，FWU能力与整体叶片表面润湿性之间没有明显的联系。相反，由于亲水性叶片表面微区，几种Crassula物种的分层雕刻叶片表面可能会促进FWU，甚至在看似疏水的物种中。总的来说,这些结果证实了在Crassula中，由线虫介导的FWU的生态生理相关性，并重申了大气湿度对某些适应干旱的植物群体的重要性。
