The air as a means to assess plant biodiversity in Alpine environments

Alpine environments are particularly susceptible to the impacts of global change with climate warming causing significant shifts in plant communities. Many plants reproduce by dispersing pollen and spores through the air, each with unique micromorphological traits specific to their species. We aim to explore the air as an innovative substrate for plant biodiversity monitoring in alpine environments. Air deposition samples from four alpine sites in Trentino: Rifugio Larcher al Cevedale, Rifugio Rosetta, Rifugio Val di Fumo, and Rifugio Altissimo are used both for traditional microscopic analysis of plant propagules, and the analysis of environmental DNA (eDNA). By adopting DNA metabarcoding methodology, higher taxonomic resolution of airborne plant biodiversity in the bioaerosol can be achieved than with current standards. Additionally, vegetation and floristic data were acquired at various scales from the receptor site to interpret the origins of plant bioaerosols. At Rifugio Larcher, for example, 21 pollen taxa were identified with the optical microscope at a magnification of 400 x in 2023. 84% of the total pollen recorded were of herbaceous and 16% of woody plants. In five plots (total area 20 m2), a total of 46 vascular plant taxa were recorded. Ten species identified in the vegetation analysis were absent in the air sample. Conversely, the air samples contained pollen from 13 taxa originating outside the local area. In parallel, a protocol for eDNA extraction and amplification has been developed, as well as a customized reference database targeting the ITS1 and ITS2 regions for identifying pollen. In the open alpine environment airborne pollen generally mirrors the local flora. Nonetheless, a portion of the biodiversity originates from distant or lower-altitude sources. Preliminary results from the molecular analysis of the air samples validated with vegetation data indicate that eDNA can be a powerful tool to assess plant biodiversity.