Changes in Foliar Water Uptake Caused by Water Stress in Cattleya Lindl. (Orchidaceae)

In response to water restrictions imposed by the epiphytic environment, orchids have developed strategies to increase water-use efficiency, such as the expression of Crassulacean Acid Metabolism (CAM) and the foliar water uptake (FWU). In a climate change scenario, FWU may emerge as a strategy to reduce water stress during drought. In this study, we propose that, in Cattleya forbesii Lindl. and Cattleya guttata Lindl., drought alters the leaf water balance, increases CAM expression, and may consequently increase the FWU rate. To test this hypothesis, drought stress was induced by restricting water for 30 days in C. forbesii (n = 4) and C. guttata (n = 6). After that, we evaluated the relative water content (RWC), overnight organic acid accumulation (ΔH⁺), and FWU capacity. To verify the pathway of water entry into the leaves, we used the apoplastic marker Lucifer Yellow. We observed that in both Cattleya species, drought impacted leaf water status, photosynthetic activity, and FWU capacity. After water restriction, the leaf water status decreased, impairing photosynthetic activity in both species (lower RWC, potential quantum yield of PSII, and quantum efficiency under light-adapted conditions), whereas nonphotochemical quenching increased. Despite minor changes in ΔH⁺ values, FWU increased following drought, partially supporting our hypothesis. In both Cattleya species, LY solution diffused through the epidermis and reached the mesophyll; however, in C. guttata, this occurred only through the abaxial epidermis. These results demonstrate that FWU may serve as a strategy for Cattleya species to cope with water scarcity intensified by drought periods.