Swiss Federal Institute for Forest, Snow and Landscape Research WSL, 8903 Birmensdorf, Switzerland.
Departamento de Sistemas y Recursos Naturales, Universidad Politécnica de Madrid, 28034 Madrid, Spain.
Tree Physiol. 2021 Sep 10;41(9):1611-1626. doi: 10.1093/treephys/tpab046.
The Canary Islands, an archipelago east of Morocco's Atlantic coast, present steep altitudinal gradients covering various climatic zones from hot deserts to subalpine Mediterranean, passing through fog-influenced cloud forests. Unlike the majority of the Canarian flora, Pinus canariensis C. Sm. ex DC. in Buch grow along most of these gradients, allowing the study of plant functioning in contrasting ecosystems. Here we assess the water sources (precipitation, fog) of P. canariensis and its physiological behavior in its different natural environments. We analyzed carbon and oxygen isotope ratios of water and organics from atmosphere, soil and different plant organs and tissues (including 10-year annual time series of tree-ring cellulose) of six sites from 480 to 1990 m above sea level on the Canary Island La Palma. We found a decreasing δ18O trend in source water that was overridden by an increasing δ18O trend in needle water, leaf assimilates and tree-ring cellulose with increasing altitude, suggesting site-specific tree physiological responses to relative humidity. Fog-influenced and fog-free sites showed similar δ13C values, suggesting photosynthetic activity to be limited by stomatal closure and irradiance at certain periods. In addition, we observed an 18O-depletion (fog-free and timberline sites) and 13C-depletion (fog-influenced and fog-free sites) in latewood compared with earlywood caused by seasonal differences in: (i) water uptake (i.e., deeper ground water during summer drought, fog water frequency and interception) and (ii) meteorological conditions (stem radial growth and latewood δ18O correlated with winter precipitation). In addition, we found evidence for foliar water uptake and strong isotopic gradients along the pine needle axis in water and assimilates. These gradients are likely the reason for an unexpected underestimation of pine needle water δ18O when applying standard leaf water δ18O models. Our results indicate that soil water availability and air humidity conditions are the main drivers of the physiological behavior of pine along the Canary Island's altitudinal gradients.
加那利群岛位于摩洛哥大西洋海岸以东，呈东西走向，群岛地形起伏，海拔梯度变化较大，从炎热干旱的沙漠到高山地中海气候，再到云雾缭绕的森林，各种气候带应有尽有。不同于加那利群岛的大多数植物，卡纳利松（Pinus canariensis C. Sm. ex DC. in Buch）生长在这些海拔梯度的大部分地区，这为研究不同生态系统中植物的功能提供了可能。在这里，我们评估了不同自然环境中卡纳利松的水分来源（降水、雾）及其生理行为。我们分析了来自大气、土壤和不同植物器官和组织（包括 10 年树轮纤维素的时间序列）的水和有机物中的碳和氧同位素比值，这些样本取自加那利群岛拉帕尔马岛上的 6 个海拔 480 至 1990 米的站点。结果发现，水源中的δ18O 呈逐渐减少的趋势，但随着海拔的升高，针叶水、叶片同化产物和树轮纤维素中的δ18O 呈逐渐增加的趋势，这表明不同地点的树木对空气湿度具有特定的生理响应。有雾和无雾的地点显示出相似的δ13C 值，这表明光合作用受到气孔关闭和一定时期内光照的限制。此外，我们观察到晚材比早材具有更明显的δ18O 和δ13C 消耗（无雾和林线地点），这是由季节性差异引起的：（i）水分吸收（即夏季干旱时地下水较深、雾水频率和截留）和（ii）气象条件（茎径向生长和晚材 δ18O 与冬季降水相关）。此外，我们发现叶片水分吸收的证据，以及在针叶轴上水分和同化产物中的强同位素梯度。这些梯度可能是在应用标准叶片水δ18O 模型时，对针叶水δ18O 低估的原因。我们的研究结果表明，土壤水分供应和空气湿度条件是影响松树在加那利群岛海拔梯度上生理行为的主要因素。
