Format: ORAL

Frederic Lens1,2, Timo Conradi3, Renske E. Onstein1,4, Helge Bruelheide4,5, Alex Zizka1,6

1 Naturalis Biodiversity Center, Leiden, The Netherlands 2 Institute of Biology Leiden, Leiden University, Leiden, The Netherlands 3 Plant Ecology, Faculty of Biology, Chemistry and Earth Sciences, Bayreuth University 4 German Centre for Integrative Biodiversity Research Halle-Jena-Leipzig (iDiv), Leipzig, Germany 5 Institute of Biology/Geobotany and Botanical Garden, Martin Luther University Halle-Wittenberg, Halle (Saale), Germany 6 Department of Biology, Philipps-University Marburg, Marburg, Germany

Wood formation is a fundamental evolutionary innovation that gave rise to countless woody species (trees and shrubs), offering crucial ecosystem services such as carbon storage and its associated climatic feedback. Most of these species only have woody ancestors, whereas other lineages have independently evolved woodiness from non-woody (herbaceous) ancestors throughout evolutionary history. However, what drives species to become woody and why have so many unrelated herbaceous lineages evolved to new woody species? These key questions have baffled scientists since Darwin, but scientific information has been too fragmented to develop hypotheses that could be rigorously tested. Therefore, we have compiled a unique woodiness database in flowering plants, showing that most woody species with herbaceous ancestors occur in regions with recurrent drought cycles. This has laid the foundation for a novel hypothesis, proposing drought as the major driver of most transitions towards woodiness. We are testing this concept on islands and continents (1) by inferring via modelling whether there is a positive correlation between woodiness and drought, and (2) by assessing via experiments whether woody species with herbaceous ancestors are consistently more drought-tolerant than their herbaceous relatives. By bridging evolutionary biology and ecophysiology, this work shows increasing evidence for a novel strategy that reveals how plants respond to drought stress in a world facing global change.