Cloud water interception and resilience of tropical montane bryophytes to climate change in cloud forests of La Reunion

Tropical montane cloud forests (TMCFs) are characterized by frequent cloud immersion, host a high diversity of global biodiversity and provide vital ecosystem services to insular populations. Climate change on islands, is expected to both raise the cloud height base as a result of temperature increase and to increase the frequency of extreme events like drought. Bryophytes contribute a significant biomass in these systems yet the role of cloud water and the resilience of bryophytes to drought in island TMCFs is still poorly known. In La Reunion, we implemented a novel method to follow cloud water interception by bryophytes in the TMCF using in situlysimeters. We showed that two abundant TMCF liverworts possess an excellent ability to intercept and store cloud water, and that stored water fluctuated according to climatic conditions. In order to better understand the ecophysiology of TMCF bryophytes, we examined chlorophyll fluorescence, under laboratory conditions, for 16 bryophyte species in response to dehydration and rehydration. This was accompanied by measurements of water retention capacity and relative water content of each species. Highest Water Retention Capacity and Relative Water Content were recorded for Sphagnumsp ( 2174 %: 91,37 %) and Anthocerossp ( 1540 %; 7815 %). Dry down curves showed that species with high water storage capacity are favored by maintaining longer optimal photosynthetic activity. After one week of desiccation, half of the species could recover 50 % of their optimal photosynthetic activity within 24 h of rehydration. Most species, after 7 weeks of desiccation, could not recover their original photosynthetic activity after rehydration. These experiments highlight the presence of various strategies for managing desiccation by TMCF bryophytes at the microhabitat level. Bryophytes inhabiting the TMCF, exhibit a strong strategy in either tolerance or drought avoidance or a combination of both strategies, indicating a better adaptation to drought than expected. However, impact of repetitive drought on the physiology of the TMCF species remains unknown. The multiplicity of responses recorded for TMCF bryophytes regarding their physiology and life forms indicate that climate change will have distinct impacts on species