Desiccation Tolerance and Global Change: Implications for Tropical Bryophytes in Lowland Forests

Global change puts an increasing pressure on tropical forests and their inherent diversity by the risk of longer droughts and drier microclimatic conditions within the forest. How organisms will respond is uncertain, especially for organisms highly depending on their microclimatic environment such as bryophytes. An adequate tolerance to desiccation is important to face these changes, however, little is known for tropical bryophytes. We investigated for the first time the desiccation tolerance of epiphytic bryophytes from contrasting microsites at the tropical lowland forest in French Guiana. Using chlorophyll-fluorescence (F v /F m ) as an indicator of recovery, we tested: (1) desiccation tolerance for short (3 d) and long (9 d) desiccation events; (2) different desiccation intensities; and (3) recovery by rehydration with water vapor. Species from the canopy were well adapted to desiccation events. Thirteen of 18 species maintained more than 75 percent of their photosynthetic capacity after recovery at the strongest desiccation treatment of 9 d at 43 percent relative humidity (RH). In contrast, species from the understory were sensitive and withstood desiccation only at humid conditions of 75 percent RH and higher. The photosystem of the studied bryophytes was reactivated efficiently in equilibration with water vapor only—a yet neglected phenomenon in bryology. A novel introduced desiccation tolerance index allows global comparison of desiccation tolerances and highlights the sensitivity of understory species. Our results suggest that decreasing humidity caused by climate change and forest degradation could be a concerning threat for understory species.