Light and Moisture Content as Determinants of Photosynthetic Activity in Southern Appalachian Mosses from Open and Shaded Habitats

The Southern Appalachian Mountains (SAM) are one of the most bryophyte-rich ecosystems in North America. This study investigates the ecophysiology of four moss species from the SAM, two acrocarpous mosses from open habitats (Ceratodon purpureus and Polytrichum juniperinum) and two pleurocarpous species from forest understories (Thuidium delicatulum and Hypnum imponens). Field sites were established to measure microclimatic conditions and physiological attributes of the mosses. Laboratory experiments included gas exchange measurements using a custom moss cuvette, moisture release curves, and dark-adapted fluorescence (Fv/Fm) as an indicator of high light photoinhibition. Moisture response curves, gas exchange measurements, Fv/Fm, and chlorophyll amounts were also measured in the field. Open-habitat mosses exhibited higher photosynthetic rates, light saturation points, and water use efficiencies than understory forest mosses. Open-habitat mosses could maintain photosynthesis at lower relative water contents for longer periods than understory species. Chlorophyll content was higher in open habitat mosses with little seasonal variation. Dark-adapted Fv/Fm measurements showed that understory mosses displayed lower tolerance to photoinhibition compared to open-habitat species. These findings highlight the physiological adaptations of SAM mosses to their respective habitats and can serve as baseline observations when considering the potential impacts of climate change on their ecological roles and distribution.<p></p>