The high adaptive potential of Abies alba Mill. seedlings – biochemical and physiological studies of succession along the environmental gradient of a Cambrian quarry

Abies alba Mill. (silver fir) needs specific soil and humidity conditions and seedlings are vulnerable to climatic extremes. Surprisingly, successful seedling establishment has been observed in disturbed habitats like active quarries. We compared 2-year old fir seedlings in three habitats—natural fir forest, disturbed forest, and exposed quarry—to explore the biochemical features that help them endure the first stages of succession in harsh environments. We assessed a range of parameters including reactive oxygen species (ROS) levels, antioxidant activity (2,2-diphenyl-1-picrylhydrazyl reduction), foliar pigments (chlorophylls and carotenoids), C and N contents, nonstructural carbohydrates, phenolics, and cell wall components analyzed via Fourier Transform Infrared (FTIR) spectroscopy, as well as ectomycorrhizal colonization and diversity. The analysis indicated that the fir seedlings were in unexpectedly good physiological condition despite the environmental constraints. Continuous exposure to harsh conditions (stony soils poor in C and N, extreme insolation, potential drought/flooding stress, etc.) was only slightly associated with ROS and antioxidant levels, roots of seedlings were fully mycorrhized, and their roots did not express signals of severe oxidative stress. Only a few seedling features clearly followed the environmental gradient; C (%), ectomycorrhizal fungal richness in roots, and total antioxidant content in stems decreased in harsh environments. Despite the lower chlorophyll levels, seedlings from the quarry had no decrease in C or N foliar levels. These firs did not have impaired N- or C-compound levels. Quarry seedlings had the highest nonstructural carbohydrates in needles and roots, protective foliar shifts (more carotenoids), and stronger stems (more structural carbohydrates, especially lignin). These findings demonstrate strong acclimatization capacity of A. alba seedlings and suggest the existence of stabilizing physiological mechanisms supporting survival in disturbed environments.