Physiological Indicators for Post-Translocation Monitoring of Salix lapponum in Natural vs. Degraded Peatlands

The progressive degradation of natural habitats, driven by anthropogenic pressures and climate change, constitutes one of the most serious threats to biodiversity. Peatland ecosystems, along with the valuable plant species associated with them, are particularly vulnerable to these processes. Salix lapponum, a glacial relict species, is undergoing a drastic decline in both its range and population size across Poland and Europe. This emphasizes the need for the implementation of conservation measures, including species translocation, as well as the development of effective methods for monitoring plant condition following introduction. The aim of this study was to evaluate the usefulness of selected physiological indicators for the rapid and reliable assessment of plant condition in active conservation efforts. The experimental material consisted of S. lapponum plantlets derived from tissue culture, which were introduced into five experimental sites in eastern Poland, differing in habitat conditions. Over two growing seasons, chlorophyll fluorescence parameters (F0, Fm, Fv/Fm), the content of photosynthetic pigments and anthocyanins, relative water content, guaiacol peroxidase activity, and the presence of reactive oxygen species were analyzed. The results revealed clear seasonal variability in most of the studied physiological parameters, as well as their differentiation across habitat conditions. The highest sensitivity to environmental changes was observed for indicators related to photosynthetic performance (Fv/Fm), tissue hydration status (RWC), and enzymatic activity. Declines in photosystem II efficiency at the beginning of the growing season, reflected in Fv/Fm values decreasing to 0.47–0.49 indicate transient stress conditions in plants. Simultaneously, variation in relative water content (52–90%) and peroxidase activity reflects differences in water availability and the intensity of environmental stress across habitats. The findings confirm that selected physiological indicators can serve as effective tools for the early monitoring of plant condition and for assessing the success of S. lapponum translocation.