Contrasting Photochemical Stability and Oxidative Injury Shape Drought Responses in Ferns and Mosses

Drought increasingly threatens terrestrial vegetation, whereas current syntheses remain disproportionately focused on seed plants. Ferns and mosses provide a useful contrast because they represent distinct hydration strategies among early-diverging land plants. We compiled 3272 paired observations from 46 drought experiments covering 35 fern species and 41 moss species to compare responses in water status, photosynthesis, chlorophyll fluorescence, oxidative stress, osmotic adjustment, abscisic acid, and growth. Drought reduced physiological performance in both groups, but mosses showed a greater mean decline than ferns. Ferns maintained stable maximum quantum yield and increased nonphotochemical quenching despite reduced pigment content and carbon assimilation, suggesting stronger photoprotective regulation. In contrast, mosses showed coordinated declines in maximum fluorescence, effective PSII yield, and maximum quantum yield, together with elevated minimum fluorescence, indicating direct PSII impairment. Oxidative damage, osmolyte accumulation, and growth suppression were also stronger in mosses. Within ferns, drought sensitivity was concentrated in epiphytic species, especially obligate, canopy, tank-forming, and xerophytic groups. Fern responses were partly explained by provenance climate, drought duration, and specific leaf area. Overall, within the species and experimental conditions represented in the current dataset, ferns largely maintain photochemical stability through photoregulation, whereas mosses shift more rapidly toward PSII impairment, oxidative injury, and growth suppression, highlighting vulnerable components of moisture-dependent ecosystems under intensifying drought.