Drought-induced water use patterns in epiphytic ferns and orchids of the Hainan tropical cloud forest, South China

Abstract

Understanding how epiphytic vascular plants respond to drought is essential for elucidating the potential mechanisms that may contribute to their resilience in the context of global climate change. Despite numerous studies have estimated tropical epiphytic vascular plants’ water source and use efficiency, their response to drought induced water scarcity poorly understood. We conducted an in-situ water reduction control experiment (i.e., controlling rain and fog water, each with three treatments) on epiphytic vascular plant communities in a biodiverse hotspots region of Hainan tropical cloud forest. We then investigated the water sources and water use efficiency (WUE) of epiphytic vascular plants under different drought gradients. We found a significant seasonal variation in water sources: 63 %–67 % in the dry season (November to April of the next year) and 64 %–70 % in the wet season (May to October) came from fog and rain, respectively In the wet season, epiphytic ferns utilized 39 % fog and 61 % rain, while orchids utilized 31 % fog and 69 % rain. Ferns absorbed significantly more fog water than orchids under all drought gradients. In the dry season, 63 % of the water in epiphytic ferns and 64 % in orchids originated from fog, while 37 % and 36 % from rain for ephiphytic ferns and orchids respectively. The WUE of ferns was significantly higher than that of orchids under all drought gradients. These findings reveal that both epiphytic vascular plant communities and epiphytic taxa display selective and complementary water uptake strategies, with distinct differences in water use strategy between epiphytic ferns and orchids.