Format: ORAL

Daniela Aros-Mualin1, Amanda Taylor2, Patrick Weigelt2, Michael Kessler1

1 Department of Systematics and Evolutionary Botany, University of Zurich, Switzerland 2 Faculty of Forest Sciences & Forest Ecology, University of Göttingen, Germany

The colonization of land by plants strongly depended on their ability optimize the use of water. Vascular plants have successfully colonized a broad range of habitats, but their diversity is lower under physiologically stressful conditions. Ferns, the second most diverse extant land plant group, exhibits disparate global patterns of species richness when compared to angiosperms. This contrast becomes more evident under water-limited environments, where the diversity of ferns sharply declines. To understand this disparity, we combined greenhouse experiments of water use efficiency (WUE) with studies of global macroecological distribution patterns. In the greenhouse, we compared WUE, quantified as the biomass produced per unit of water usage, of 12 fern and 12 angiosperm species, encompassing both terrestrial and epiphytic ones. We found that among terrestrial species, ferns exhibit lower WUE and consequently higher water loss compared to angiosperms. At the macroecological scale, this is reflected by an increase in the proportion of ferns relative to angiosperms as water availability increases. Conversely, fern and angiosperm epiphytes had a comparable WUE in the greenhouse, which at the macroecological scale is reflected by a constant proportion of fern richness in relation to water availability. These findings reveal the key role of water in shaping the competitive dynamics between ferns and angiosperms, and their diversity patterns. Moreover, it suggests that terrestrial ferns serve as potential early indicators of climate change.