Department of Forestry and Natural Resources, University of Kentucky, Lexington, 40546, KY, USA.
Division of Natural Resources, Channel Islands National Park, Ventura, 93001, CA, USA.
Am J Bot. 2024 Oct;111(10):e16423. doi: 10.1002/ajb2.16423. Epub 2024 Oct 11.
Vascular epiphytes of tropical montane cloud forests are vulnerable to climate change, particularly as cloud bases elevate and reduce atmospheric inputs to the system. However, studies have generally focused on epiphytes in contiguous forests, with little research being done on epiphytes on isolated pasture trees. We investigated water relations of pasture-tree epiphytes at three sites located below and above the elevation of the average cloud base in Monteverde, Costa Rica.
We measured sap velocity and four microclimate variables in both the dry and wet season of 2018. We also measured functional traits, including pressure volume (PV) curves, predawn/midday water potential, and various lab-based water relations traits. We used linear mixed models to assess the correlation between microclimate and sap velocity in both seasons and ANOVA to assess the variation in PV curve and water potential variables.
The turgor loss point generally increased from the wettest to driest site. However, this trend was driven primarily by the increasing prevalence of leaf succulence at drier sites. Microclimatic variables correlated strongly with sap velocity in the wet season, but low soil moisture availability caused this correlation to break down during the dry season.
Our results emphasize the vulnerability of cloud forest epiphytes to rising cloud bases. This vulnerability may be more severe in pasture trees that lack the potential buffer of surrounding forest, but additional research that directly compares the canopy microclimate conditions between forest and pasture trees is needed to confirm this possibility.
热带山地云雾林的附生植物易受气候变化影响，特别是当云层底部抬升并减少对系统的大气输入时。然而，研究通常集中在连续森林中的附生植物上，而对孤立的牧树附生植物的研究甚少。我们调查了哥斯达黎加蒙特维多三个地点的牧树附生植物的水分关系，这些地点位于平均云层底部海拔以下和以上。
我们在 2018 年的旱季和雨季测量了 sap 速度和四个小气候变量。我们还测量了功能性状，包括压力体积（PV）曲线、晨/午间水势和各种基于实验室的水分关系性状。我们使用线性混合模型来评估两个季节中小气候和 sap 速度之间的相关性，并使用 ANOVA 来评估 PV 曲线和水势变量的变化。
膨压损失点通常从最潮湿的地点到最干燥的地点增加。然而，这种趋势主要是由较干燥地点的叶片多汁性的增加所驱动。在雨季，微气候变量与 sap 速度密切相关，但在旱季，由于土壤水分供应不足，这种相关性破裂。
我们的研究结果强调了云雾林附生植物对云层底部上升的脆弱性。对于缺乏周围森林潜在缓冲的牧树附生植物来说，这种脆弱性可能更为严重，但需要进行直接比较森林和牧树附生植物之间树冠微气候条件的额外研究来证实这种可能性。
