A Worldwide Survey Reveals Four Distinct Patterns of Photochemical Dehydration Tolerance Across Land Plant Phylogeny

The dehydration tolerance of photosynthetic tissues varies greatly along land plant's phylogeny. We investigated the photochemical response to severe dehydration and subsequent rehydration in 318 species representing the major terrestrial biomes and photosynthetic lineages: lichens, bryophytes, pteridophytes and spermatophytes. Using a standardized portable dehydration test with the maximum photochemical efficiency of PSII (F_v/F_m) as indicator, data meeting two key criteria were analyzed: (1) optimal physiological conditions before dehydration and (2) achieving relative water contents (RWC) below 25% at the dehydration stage (with approximately half dropping further to 5%-15%). Lichens and mosses displayed the highest overall Fv/Fm recovery after dehydration, whereas lower tolerance was observed in the other plant groups. Four distinct photochemical responses to dehydration emerged: dehydration-sensitive (61.2%), rehydration-sensitive (18.6%), dehydration-tolerant (13.6%), and dehydration-resistant (6.5%). Pteridophytes and spermatophytes predominantly exhibited dehydration- or rehydration-sensitive responses, whereas dehydration-tolerant dynamics were mainly observed in mosses and resurrection plants. Dehydration-resistant patterns were rare and occurred particularly in polar and high-altitude angiosperms such as Colobanthus quitensis, Deschampsia antarctica and Pozoa coriacea. These findings highlight the evolutionary divergence of dehydration tolerance strategies across the land plant phylogeny and provide insights into the underlying photochemical mechanisms.