Data_Sheet_1_Resisting Aridification: Adaptation of Sap Conduction Performance in Moroccan Wild Olive Subspecies Distributed Over an Aridity Gradient.docx

In the current context of global change, the increasing frequency and the length of drought periods are testing the resistance capacities of plants of dry habitats. However, although the adaptation of plants to drought has been widely studied, the anatomical features of wood influencing the functional responses of plants to drought are still lacking at the intraspecific level, especially for species with a wide geographical distribution. As a result, we have studied the variation of wood anatomical traits related to sap conduction (i.e., vessel surface area, vessel density, and number of vessels joined by radial file) in two wild olive subspecies distributed in Morocco (i.e., Olea europaea subsp. europaea. var. sylvestris and Olea europaea subsp. maroccana), in relation to various drought conditions. This functional study, based on wood trait measurements of 351 samples from 130 trees and 13 populations, explores potential sap conduction in relation to environmental parameters and as a result, strategies to resist water stress. We found that (1) branch diameter (BD) captured 78% of total wood trait variation, (2) vessel size (SVS) expressed 32% of intraspecific variation according to cambium age, and (3) the positive relationship between SVS and BD could be explained by climate type, vegetation cover changes, and therefore available water resources. Taking into consideration the diameter of the branch as the main factor of anatomical variation, established reaction norms (linear models) at the intrapopulation scale of vessel lumen area according to aridity show for the first time how the functioning of the cambium modulates and controls sap conduction, according to aridity and thus available water resources. They pinpoint the risks incurred by the wild olive tree in the perspective of a dramatic increase in aridity, in particular, the inability of the cambium to produce large enough vessels to efficiently transport sap and irrigate the leaves. Finally, this study opens new and interesting avenues for studying at a Mediterranean scale, the resistance and the vulnerability of wild forms and cultivated varieties of olive to heterogeneous and changing environmental conditions.在当前全球变化的背景下，干旱期的频发与持续时长不断延长，正不断考验着干旱生境植物的抗性能力。尽管学界已对植物适应干旱的机制展开了广泛研究，但影响植物对干旱的功能响应的木材解剖性状（wood anatomical traits），在种内水平（intraspecific level）上仍存在研究空白，尤其是针对地理分布范围较广的物种。为此，我们以分布于摩洛哥的两个野生油橄榄亚种（即Olea europaea subsp. europaea var. sylvestris与Olea europaea subsp. maroccana）为研究对象，针对不同干旱条件，分析了与汁液传导（sap conduction）相关的木材解剖性状变异——包括导管表面积（vessel surface area）、导管密度（vessel density）以及径向行列（radial file）连接的导管数量。 本项基于130株树木、13个种群共351份样本的木材性状测量的功能研究，探讨了潜在汁液传导与环境参数的关联，并由此揭示了植物抵御水分胁迫（water stress）的策略。研究发现：（1）枝条直径（branch diameter, BD）可解释78%的木材性状总变异；（2）导管尺寸（vessel size, SVS）可依据形成层年龄（cambium age）解释32%的种内变异（intraspecific variation）；（3）导管尺寸与枝条直径间的正相关关系，可通过气候类型、植被覆盖变化及由此决定的可用水资源量加以阐释。 在将枝条直径视作解剖变异的核心影响因子后，本研究基于种群内尺度（intrapopulation scale）建立了导管腔面积（vessel lumen area）随干旱度（aridity）变化的反应规范（reaction norms，即线性模型linear models），首次揭示了形成层如何依据干旱度及由此决定的可用水资源量，调控并维持汁液传导功能。研究明确了野生油橄榄在干旱度显著加剧的背景下面临的风险，具体表现为形成层无法生成足够大的导管以高效运输汁液、为叶片供水。 最后，本研究为地中海尺度下探究野生型与栽培型橄榄对异质性且不断变化的环境条件的抗性与脆弱性，开辟了全新且极具价值的研究方向。