Linking biosurface reactivity and photosynthesis to investigate Sphagnum mosses as peatland engineers

O_LISphagnum mosses regulate peatland carbon cycling, hydrology, nutrient dynamics, and structure. We investigated the link between Sphagnum surface chemistry and photosynthetic efficiency, and the combined effects of pH and waterlogging on photosynthesis, key mechanisms for peatland functioning but still poorly understood. C_LIO_LIWe quantified biosorption potential and functional groups in 20 field collected and in 4 axenically cloned Sphagnum species via titrations. Gas exchange and chlorophyll fluorescence measurements were performed in 5 representative species under submerged conditions across a pH gradient. C_LIO_LIThe 20 Sphagnum species share a basic surface chemistry, but they differ in surface charge and functional group abundance, with an overall greater biosorption potential in the subgenera Acutifolia and Sphagnum. Photosynthesis is species- and pH-dependent, influenced by surface functional-group composition, with phosphoryl and carboxyl groups enhancing CO2 assimilation. Sphagnum palustre emerges as a generalist, stress-tolerant species, maintaining stable photosynthesis and photoprotection across pH ranges. In-vitro cultivation reduces surface reactivity and interspecific differentiation but preserves fundamental Sphagnum surface chemistry. C_LIO_LIThese results highlight the interplay between chemical reactivity, photosynthetic performance, and ecological adaptation in Sphagnum. Sphagnum chemical traits and photosynthetic plasticity enable survival under variable pH, waterlogging, and nutrient conditions, with clones providing reliable models for research and applications. C_LI