SOS - Success of Salix shrubs encroachment leading to a major vegetation and landscape change in the Italian Alps
ProgettoProject aims and rationale
Shrub encroachment is a widespread response to climate change (CC) in which the role of microbiome in aiding plant adaptation still needs specific investigations. In the European Alps a new successional pathway, likely triggering major vegetation changes, is occurring with the encroachment of several species of hygrophilous pioneer Salix shrubs into a range of habitats from subalpine shrublands to alpine grasslands and snowbeds, across a 1000 m elevation gradient from the subalpine to the nival belt. The project SOS aims to understand the mechanisms of the success of these encroaching Salix shrubs compared to the target species of the encroached habitats (Rhododendron ferrugineum for the subalpine shrublands; Carex curvula for the alpine grasslands; Salix herbacea for the snowbeds habitat) by addressing three specific issues: a) plant traits, phenology, and photosynthetic performances; b) soil microbiota, including root mycorrhizae: c) soil physicochemical characteristics.
We aim to assess through multidisciplinary analyses the natural variability of the environmental conditions associated with the five more abundant Salix encroaching shrubs compared with those of the three target species of the encroached habitats in three study areas analysing: plant leaf traits, photosynthetic performances, plant phenology, rhizosphere and soil microbiota through next-generation sequencing, soil physicochemical characteristics.
Field Activities and Sampling
The field activities were performed on 150 marked individuals of the selected species at the three study sites. Across two growing seasons (2024, 2025) we measured a total number of 10728 and 22019 records of photosynthetic performances, collected 697 and 962 samples of leaves for the assessment of plant traits (leaf area, leaf dry matter content, specific leaf area), 300 samples of sterile soil and root samples underneath all the marked individuals to analyse soil and root microbiota, and 150 samples to assess soil physicochemical characteristics.
Results
The environmental data showed that the leaf conditions were slightly different between the two years for all species with higher PAR (photosynthetic active radiation), comparable temperature and lower humidity in 2025 compared to 2024. All species exhibited higher values of the effective photosynthetic performance, specific leaf area and leaf area in 2025. All Salix species exhibited effective photosynthetic performance higher or similar to those of the encroached species. Leaf area and the specific leaf area were higher in 2025 for all species, coherently with the higher effective photosynthetic performance observed in 2025, while leaf size was comparable between the two years for all species. Encroaching species exhibited larger leaf area and larger specific leaf area than the encroached species.
Microbiological analyses assessed the initial patterns suggesting that both site environment and host identity can influence specific bacterial groups within a common baseline alpine soil community. Further analyses are still ongoing at more detailed taxonomic level in the next months. The soil data highlight differences in soil chemistry among the selected sites and related also the elevation gradient. The chemical analyses of soil pH, water content (%), total and organic carbon, total nitrogen, are still ongoing and are planned to be completed in the next months.
Shrub encroachment is a widespread response to climate change (CC) in which the role of microbiome in aiding plant adaptation still needs specific investigations. In the European Alps a new successional pathway, likely triggering major vegetation changes, is occurring with the encroachment of several species of hygrophilous pioneer Salix shrubs into a range of habitats from subalpine shrublands to alpine grasslands and snowbeds, across a 1000 m elevation gradient from the subalpine to the nival belt. The project SOS aims to understand the mechanisms of the success of these encroaching Salix shrubs compared to the target species of the encroached habitats (Rhododendron ferrugineum for the subalpine shrublands; Carex curvula for the alpine grasslands; Salix herbacea for the snowbeds habitat) by addressing three specific issues: a) plant traits, phenology, and photosynthetic performances; b) soil microbiota, including root mycorrhizae: c) soil physicochemical characteristics.
We aim to assess through multidisciplinary analyses the natural variability of the environmental conditions associated with the five more abundant Salix encroaching shrubs compared with those of the three target species of the encroached habitats in three study areas analysing: plant leaf traits, photosynthetic performances, plant phenology, rhizosphere and soil microbiota through next-generation sequencing, soil physicochemical characteristics.
Field Activities and Sampling
The field activities were performed on 150 marked individuals of the selected species at the three study sites. Across two growing seasons (2024, 2025) we measured a total number of 10728 and 22019 records of photosynthetic performances, collected 697 and 962 samples of leaves for the assessment of plant traits (leaf area, leaf dry matter content, specific leaf area), 300 samples of sterile soil and root samples underneath all the marked individuals to analyse soil and root microbiota, and 150 samples to assess soil physicochemical characteristics.
Results
The environmental data showed that the leaf conditions were slightly different between the two years for all species with higher PAR (photosynthetic active radiation), comparable temperature and lower humidity in 2025 compared to 2024. All species exhibited higher values of the effective photosynthetic performance, specific leaf area and leaf area in 2025. All Salix species exhibited effective photosynthetic performance higher or similar to those of the encroached species. Leaf area and the specific leaf area were higher in 2025 for all species, coherently with the higher effective photosynthetic performance observed in 2025, while leaf size was comparable between the two years for all species. Encroaching species exhibited larger leaf area and larger specific leaf area than the encroached species.
Microbiological analyses assessed the initial patterns suggesting that both site environment and host identity can influence specific bacterial groups within a common baseline alpine soil community. Further analyses are still ongoing at more detailed taxonomic level in the next months. The soil data highlight differences in soil chemistry among the selected sites and related also the elevation gradient. The chemical analyses of soil pH, water content (%), total and organic carbon, total nitrogen, are still ongoing and are planned to be completed in the next months.