LAUSR

PREMISE Epiphytes are abundant in ecosystems such as tropical montane cloud forests where low-lying clouds are often in contact with vegetation. Climate projections for these regions include more variability in rainfall and an increase in cloud base heights which would lead to drier conditions both in the soil and atmosphere. While recent studies have examined the effects of drought on epiphyte water relations, the influence that atmospheric moisture has, either alone or in combination with drought, on the health and performance of epiphyte communities remains unclear. METHODS We conducted a ten-week drought experiment on seven vascular epiphyte species in two shadehouses, one with warmer and drier conditions and another that was cooler and more humid. We measured water relations across control and drought-treatment groups and assessed functional traits on leaves produced during drought conditions to evaluate trait plasticity. RESULTS Epiphytes exposed to drought and drier atmospheric conditions exhibited a significant reduction in stomatal conductance and leaf water potential, and an increase in leaf dry matter content. Non-succulent epiphytes from the drier shadehouse exhibited the greatest shifts in functional traits whereas succulent epiphytes released stored leaf water to maintain water status. CONCLUSIONS Individuals in the drier shadehouse exhibited a substantial reduction in performance whereas drought-treated individuals that experienced cloud immersion displayed minimal changes in water status. Our results indicate that projected increases in the cloud base height will reduce growth and performance of epiphyte communities and that non-succulent epiphytes may be particularly vulnerable. This article is protected by copyright. All rights reserved.