Plant-related biodiversity in the Alpine air: a review

Aerobiology can provide answers on the impacts of global change on plant biodiversity. It has been recognized that alpine environments are susceptible to such changes. However, there are only a few studies worldwide addressing plant-related particle biodiversity in air samples in open areas at high elevations or high geographical latitudes. This study reviews aerobiological papers that focus on assessing plant biodiversity in environments that are either part of the alpine biome or are functionally connected to it. PubMed was searched for “pollen and alpine”; morphological studies, taxonomical studies, honey studies, fossil pollen studies, and non-English studies were excluded from the resulting papers. Further relevant studies were retrieved from bibliographic references of the same articles and from Google Scholar. Based on 48 articles reviewed, i) the air sampling; ii) the identification method; iii) the bioaerosol biodiversity in relation to alpine vegetation were analyzed. As for i), deposition sampling is the method of choice to collect the alpine bioaerosol, while only a few studies use volumetric air samplers. As for ii), the current state of the art for the identification of pollen and non-pollen palynomorphs is microscopic analysis. Yet, results from DNA metabarcoding show a higher taxonomic resolution in identifying plant taxa, than microscopic analysis alone can achieve. As for iii), the establishment of relationships between bioaerosol and plant biodiversity implies the assessment of vegetation diversity and abundance at different scales from the receptor site. Back trajectory models are employed to trace the origin of extra local, long-distance sources. On the whole, the alpine bioaerosol mirrors the vegetation of wind-pollinated taxa from the immediate receptor site, e.g. herbaceous such as Poaceae, Cyperaceae, Juncaceae, and ferns. Entomophilous taxa, in contrast, are underrepresented. The biodiversity from the alpine air, however, does not only originate from local sources but also from extra-local, regional, and often over-regional areas. For the Eurosiberian plant region, the articles reviewed consistently report pollen from woody plants (Pinus, Picea, Corylus, Betula) above the timberline. Microscale air currents (0 - 2 km) cause the influx from around and below the timberline into the alpine air at the receptor site. Besides, mesoscale air masses (2 - 200 km) including topography-driven convections, thunderstorms, nighttime depositions as well as long-distance transport events (200 - 2000 km) add taxa to the bioaerosol. Knowledge on the composition of the plant bioaerosol in alpine environments facilitates the reconstruction of past climate, models of climate change scenarios, the interpretation of gene flow, and the genetic makeup of populations. Such is a valuable tool for plant conservation management in alpine environments. The authors acknowledge the support of NBFC to Fondazione Edmund Mach, funded by the Italian Ministry of University and Research, PNRR, Missione 4 Componente 2, “Dalla ricerca all’impresa”, Investimento 1.4, Project CN00000033