Taylor Amanda, Burns Kevin
Ecology. 2016 Apr;97(4):819-25. doi: 10.1890/15-1322.1.
Vertical gradients of light and humidity within forest canopies are major predictors of air plant distributions. Although this pattern was first recognized over 120 years ago, few studies have considered an additional axis of resource availability, which exists radially around the trunks of trees. Here, we explored the radial distributions of mistletoes and epiphytes in relation to gradients of light and humidity around the trunks of their south-temperate host trees. Additionally, we correlated microclimate occupancy with plant physiological responses to shifting resource availability. The radial distributions of mistletoes and epiphytes were highly directional, and related to the availability of light and humidity, respectively. Mistletoes oriented northwest, parallel to gradients of higher light intensity, temperature, and lower humidity. Comparatively, epiphytes oriented away from the sun to the southeast. The rate of CO2 assimilation in mistletoes and photochemical efficiency of epiphytes was highest in plants growing in higher light and humidity environments, respectively. However, the photosynthetic parameters of mistletoes suggest that they are also efficient at assimilating CO2 in lower light conditions. Our results bridge a key gap in our understanding of within-tree distributions of mistletoes and epiphytes, and raise further questions on the drivers of air plant distributions.
森林冠层内光照和湿度的垂直梯度是气生植物分布的主要预测因素。尽管这种模式在120多年前就首次被认识到，但很少有研究考虑到围绕树干呈放射状存在的资源可利用性的另一个维度。在这里，我们探讨了槲寄生和附生植物在其南温带寄主树木树干周围的光照和湿度梯度方面的径向分布。此外，我们将小气候占据情况与植物对资源可利用性变化的生理反应进行了关联。槲寄生和附生植物的径向分布具有高度的方向性，分别与光照和湿度的可利用性相关。槲寄生朝向西北方向，与较高光照强度、温度和较低湿度的梯度平行。相比之下，附生植物背向太阳朝向东南方向。槲寄生的二氧化碳同化速率和附生植物的光化学效率分别在生长于较高光照和湿度环境中的植物中最高。然而，槲寄生的光合参数表明它们在较低光照条件下同化二氧化碳也很高效。我们的研究结果填补了我们对槲寄生和附生植物在树内分布理解上的一个关键空白，并引发了关于气生植物分布驱动因素的进一步问题。
