Departamento de Ecología de la Biodiversidad, Instituto de Ecología, Universidad Nacional Autónoma de México, Campus Hermosillo, Hermosillo 83250, Sonora, México.
Posgrado en Ciencias Biológicas, Unidad de Posgrado, Edificio A, 1o Piso, Circuito de Posgrados, Ciudad Universitaria, Ciudad de México 04510, México.
Tree Physiol. 2023 Feb 4;43(2):221-233. doi: 10.1093/treephys/tpac114.
The drought susceptibility of woody saplings may explain their low survival in arid environments. Therefore, it is critical to determine which morphological and physiological traits are more responsive to drought among young plants. This study tested whether plant responses to experimental drought differ between two plant functional groups: the deciduous and evergreen species. We predicted that deciduous species would present a tighter stomatal control under drought, coupled with fast carbon fixation under no stress, tending toward isohydry and faster growth rates than the evergreen species. Using 1-year-old saplings from three evergreen and four deciduous Sonoran Desert tree species, we evaluated their hydraulic and gas exchange traits under three experimental irrigation conditions: high, intermediate and low water availability. We measured CO2 assimilation rates (A), stomatal conductance (gs), the level of iso-anisohydry (as the plant's ability to maintain constant their water potential) and seven morphological and growth-related traits throughout 2 months. Under high water availability, saplings reached their maximum values of A and gs, which were significantly higher for deciduous than evergreen species. Correlations among hydroscape area (HA) and leaf traits positioned species along the iso/anisohydric continuum. Deciduous species presented isohydric characteristics, including low HA, high gs, A and Huber values (HVs), and traits indicative of a faster use of resources, such as low stem-specific density (SSD) and low leaf mass per area (LMA). By contrast, evergreen species showed traits that indicate slow resource use and anisohydric behavior, such as high HA, SSD and LMA, and low gs, A and HVs. Deciduous species drastically reduced gas exchange rates in response to drought, while evergreen maintained low rates independently of drought intensity. Overall, desert saplings showed strategies concordant with the iso-anisohydric continuum and the fast-slow use of resources.
木本幼苗的耐旱性可能解释了它们在干旱环境中的低存活率。因此，确定哪些形态和生理特征对幼树的干旱更敏感是至关重要的。本研究测试了两种植物功能群（落叶和常绿物种）的植物对实验干旱的反应是否不同。我们预测，落叶物种在干旱下会表现出更紧密的气孔控制，同时在无胁迫下快速固定碳，倾向于等水势和比常绿物种更快的生长速度。使用来自三种常绿和四种索诺兰沙漠树种的 1 年生幼苗，我们在三种实验灌溉条件下评估了它们的水力和气体交换特征：高、中和低水分供应。我们测量了 CO2 同化率（A）、气孔导度（gs）、等渗-异渗（植物保持其水势不变的能力）水平以及七个形态和生长相关特征，整个过程持续 2 个月。在高水分供应下，幼苗达到了 A 和 gs 的最大值，落叶物种的最大值明显高于常绿物种。水景面积（HA）和叶片特征之间的相关性将物种沿等渗-异渗连续体定位。落叶物种表现出等渗特征，包括低 HA、高 gs、A 和胡贝尔值（HV），以及指示资源快速利用的特征，如低茎比密度（SSD）和低叶面积质量比（LMA）。相比之下，常绿物种表现出指示资源缓慢利用和异渗行为的特征，如高 HA、SSD 和 LMA，以及低 gs、A 和 HV。落叶物种在干旱时急剧降低气体交换率，而常绿物种则独立于干旱强度保持低水平。总的来说，沙漠幼苗表现出与等渗-异渗连续体和快速-缓慢资源利用一致的策略。
