Trait plasticity and adaptive strategies of vascular epiphytes to a large-scale experimental reduction of fog immersion in a tropical montane cloud forest

Premise: Tropical montane cloud forests (TMCF) are characterized by frequent fog immersion and host a rich epiphyte community. Epiphytes rely on atmospheric inputs of water, making them susceptible to reductions in fog immersion, which are predicted with climate change. Methods: We experimentally reduced the fog in a Peruvian TMCF to examine the ability of eight abundant species of vascular epiphytes in the families Orchidaceae, Bromeliaceae, Ericaceae, Dryopteridaceae, Piperaceae and Clusiaceae to respond to reduced fog immersion via plasticity in morphological and physiological traits. Key results: We found that across all species combined, fog reduction led to a decrease in stomatal length (SL) and foliar water uptake (FWU) capacity. Disterigma sp. (Ericaceae), an epiphytic shrub, reduced leaf thickness (LT) with fog reduction, likely a result of reduced water storage. Comparing across species, we found significant differences in traits related to drought tolerance, including the turgor loss point (TLP), relative water content at TLP (RWC_TLP) and osmotic potential at full saturation (π_o) indicating that two studied fern species in the Elaphoglossum genus (Dryopteridaceae) may tolerate low water potentials. Conclusion: Our results revealed that some vascular epiphyte species can adjust certain morphological and physiological traits to acclimate to reduced fog immersion. Additionally, our findings support differences in ecological strategies across epiphyte functional groups to either maximize water storage in specialized tissue or to increase drought tolerance. These results give early indications of the likely vulnerability of some epiphyte groups to projected shifts in fog immersion across TCMFs globally.