Carabajo-Hidalgo Aldemar, Sabaté Santiago, Crespo Patricio, Asbjornsen Heidi
Departamento de Recursos Hídricos y Ciencias Ambientales, Universidad de Cuenca, Campus Balzay, Víctor Manuel Albornoz y los Cerezos s/n, Cuenca 010107, Ecuador.
Departamento de Biología Evolutiva, Ecología y Ciencias Ambientales, Universitat de Barcelona, Av. Diagonal, 643, Barcelona 08028, Spain.
Tree Physiol. 2023 Dec 12;43(12):2085-2097. doi: 10.1093/treephys/tpad109.
Polylepis trees occur throughout the Andean mountain region, and it is the tree genus that grows at the highest elevation worldwide. In the humid Andes where moisture is rarely limiting, Polylepis trees must adapt to extreme environmental conditions, especially rapid fluctuations in temperature, ultraviolet radiation and vapor pressure deficit (VPD). However, Polylepis' water-use patterns remain largely unknown despite the importance of understanding their response to microclimate variation to determine their capacity to maintain resilience under future environmental change. We conducted a study in a Polylepis reticulata Kunth forest in the Ecuadorian Andes to evaluate its tree water-use dynamics and to identify the main environmental drivers of transpiration. Tree sap flow was monitored simultaneously with soil volumetric water content (VWC) and microclimate during 2 years for trees growing in forest edge and interior locations. We found that sap flow was primarily controlled by VPD and that VWC exerted a secondary role in driving sap flow dynamics. The highest values for sap flow rates were found when VPD > 0.15 kPa and VCW < 0.73 cm3 cm-3, but these threshold conditions only occurred during brief periods of time and were only found in 11% of our measurements. Moreover, these brief windows of more favorable conditions occurred more frequently in forest edge compared with forest interior locations, resulting in edge trees maintaining 46% higher sap flow compared with interior trees. Our results also suggest that P. reticulata has a low stomatal control of transpiration, as the sap flow did not decline with increasing VPD. This research provides valuable information about the potential impacts of projected future increases in VPD due to climate change on P. reticulata water-use dynamics, which include higher sap flow rates leading to greater transpirational water loss due to this species' poor stomatal control.
多鳞树分布于安第斯山脉地区，是全球生长在海拔最高处的树木属。在湿度很少成为限制因素的潮湿安第斯地区，多鳞树必须适应极端环境条件，尤其是温度、紫外线辐射和水汽压差（VPD）的快速波动。然而，尽管了解多鳞树对小气候变化的响应对于确定其在未来环境变化下保持恢复力的能力很重要，但多鳞树的水分利用模式在很大程度上仍不为人知。我们在厄瓜多尔安第斯山脉的一片多鳞树森林中开展了一项研究，以评估其树木的水分利用动态，并确定蒸腾作用的主要环境驱动因素。在两年时间里，对生长在森林边缘和内部的树木，同时监测了树干液流、土壤体积含水量（VWC）和小气候。我们发现，树干液流主要受VPD控制，VWC在驱动树干液流动态方面起次要作用。当VPD > 0.15 kPa且VCW < 0.73 cm³ cm⁻³时，树干液流速率达到最高值，但这些阈值条件只在短时间内出现，且仅在我们11%的测量中被发现。此外，与森林内部位置相比，这些更有利条件的短暂窗口期在森林边缘出现得更频繁，导致边缘树木的树干液流比内部树木高46%。我们的研究结果还表明，多鳞树对蒸腾作用的气孔控制能力较低，因为树干液流并未随着VPD的增加而下降。这项研究提供了关于气候变化导致未来VPD预计增加对多鳞树水分利用动态潜在影响的有价值信息，其中包括由于该物种气孔控制不佳，较高的树干液流速率导致更大的蒸腾水分损失。
