Departamento de Biología y Geología, Física y Química Inorgánica, Universidad Rey Juan Carlos, Móstoles, Spain.
Centro de Investigación en Ecosistemas de la Patagonia (CIEP), Camino Baguales s/n, Coyhaique, Chile.
Ann Bot. 2020 Jun 1;125(7):1101-1112. doi: 10.1093/aob/mcaa042.
Plants have the potential to adjust the configuration of their hydraulic system to maintain its function across spatial and temporal gradients. Species with wide environmental niches provide an ideal framework to assess intraspecific xylem adjustments to contrasting climates. We aimed to assess how xylem structure in the widespread species Nothofagus pumilio varies across combined gradients of temperature and moisture, and to what extent within-individual variation contributes to population responses across environmental gradients.
We characterized xylem configuration in branches of N. pumilio trees at five sites across an 18° latitudinal gradient in the Chilean Andes, sampling at four elevations per site. We measured vessel area, vessel density and the degree of vessel grouping. We also obtained vessel diameter distributions and estimated the xylem-specific hydraulic conductivity. Xylem traits were studied in the last five growth rings to account for within-individual variation.
Xylem traits responded to changes in temperature and moisture, but also to their combination. Reductions in vessel diameter and increases in vessel density suggested increased safety levels with lower temperatures at higher elevation. Vessel grouping also increased under cold and dry conditions, but changes in vessel diameter distributions across the elevational gradient were site-specific. Interestingly, the estimated xylem-specific hydraulic conductivity remained constant across elevation and latitude, and an overwhelming proportion of the variance of xylem traits was due to within-individual responses to year-to-year climatic fluctuations, rather than to site conditions.
Despite conspicuous adjustments, xylem traits were coordinated to maintain a constant hydraulic function under a wide range of conditions. This, combined with the within-individual capacity for responding to year-to-year climatic variations, may have the potential to increase forest resilience against future environmental changes.
植物具有调节其水力系统结构的潜力，以维持其在时空梯度上的功能。具有广泛环境生态位的物种为评估木质部对不同气候的种内调节提供了理想的框架。我们旨在评估广泛分布的物种 Nothofagus pumilio 的木质部结构如何在温度和湿度的综合梯度上发生变化，以及个体内变异在多大程度上导致种群对环境梯度的响应。
我们在智利安第斯山脉 18°的纬度梯度上的五个地点，在每个地点的四个海拔高度上，对 N. pumilio 树木的树枝木质部结构进行了特征描述。我们测量了导管面积、导管密度和导管群集程度。我们还获得了导管直径分布，并估计了木质部比导率。木质部特征在最后五个生长年轮中进行研究，以考虑个体内变异。
木质部特征响应于温度和湿度的变化，但也响应于它们的组合。导管直径的减小和导管密度的增加表明，在较高海拔处，低温下安全水平提高。在寒冷和干燥条件下，导管群集程度也增加，但导管直径分布的变化在不同的地点是特定的。有趣的是，估计的木质部比导率在海拔和纬度上保持不变，而木质部特征的大部分方差是由于个体对年际气候波动的响应，而不是由于地点条件。
尽管存在明显的调节，但木质部特征是协调的，以在广泛的条件下维持恒定的水力功能。这与个体对年际气候变化的响应能力相结合，可能有潜力提高森林对未来环境变化的抵抗力。
