Belluau Michaël, Shipley Bill
Ann Bot. 2017 Apr 1;119(6):1073-1084. doi: 10.1093/aob/mcw267.
Soil water availability is an important mechanism filtering plant species but the functional basis of this filtering in herbaceous dicots is poorly studied. The authors address three questions: Which physiological traits best predict different levels of drought tolerance or avoidance in herbaceous dicots? To what degree can species' habitat preferences along the gradient of soil moisture availability be predicted by their physiological responses to drought? What are the direct and indirect relationships between the physiological traits and how do they interact to determine the species' habitat preferences?
Twenty-five species of herbaceous dicots whose field distributions span a gradient of soil moisture from continually moist to dry were chosen. Under controlled conditions, watering was stopped in a treatment group, the plants were monitored until death of the above-ground tissues and compared with a control group watered at field capacity. Fourteen traits related to plant water economy were measured, including stomatal conductance, net photosynthesis and the visual wilting of leaves. Traits were then analysed using a cumulative link model and path analysis.
Five physiological traits (stomatal conductance and net photosynthesis measured at soil field capacity, water use efficiency, stomatal conductance and soil water potential measured when leaves begin to wilt) related to the ability to acquire resources (when water is not limiting) or conserve water (when it is limiting) best predicted different levels of drought tolerance or avoidance in herbaceous dicots.
Species' habitat preferences can be fairly predicted by their physiological responses to drought ( R 2 = 0·48). Strong direct and indirect relationships between the five identified traits (plus net photosynthesis at wilting and the time until death) led to synergistic and antagonistic relationship in a path analysis model. To allow better prediction of species distributions along a wetness gradient, the next step would be to link these physiological traits to more accessible functional traits.
土壤水分有效性是筛选植物物种的重要机制，但草本双子叶植物中这种筛选的功能基础研究较少。作者提出了三个问题：哪些生理特征能最好地预测草本双子叶植物不同程度的耐旱性或避旱性？根据物种对干旱的生理反应，能在多大程度上预测其在土壤水分有效性梯度上的栖息地偏好？生理特征之间的直接和间接关系是什么，它们如何相互作用以决定物种的栖息地偏好？
选择了25种草本双子叶植物，其野外分布跨越从持续湿润到干燥的土壤湿度梯度。在受控条件下，对一个处理组停止浇水，监测植物直至地上组织死亡，并与以田间持水量浇水的对照组进行比较。测量了与植物水分经济相关的14个特征，包括气孔导度、净光合作用和叶片的可视萎蔫。然后使用累积链接模型和路径分析对特征进行分析。
与获取资源（水分不限制时）或保持水分（水分限制时）能力相关的五个生理特征（在土壤田间持水量时测量的气孔导度和净光合作用、水分利用效率、叶片开始萎蔫时测量的气孔导度和土壤水势）能最好地预测草本双子叶植物不同程度的耐旱性或避旱性。
根据物种对干旱的生理反应，可以较好地预测其栖息地偏好（R² = 0·48）。在路径分析模型中，五个已确定特征（加上萎蔫时的净光合作用和死亡时间）之间强烈的直接和间接关系导致了协同和拮抗关系。为了更好地预测物种沿湿度梯度的分布，下一步是将这些生理特征与更易获取的功能特征联系起来。
