Biodiversity and plant growth-promoting traits of yeasts from alpine peatlands

Peatlands are waterlogged areas where the rate of biomass production is greater than the rate of decomposition, thus resulting in the formation of peat, a complex material that consists of partly fossilized plant residues. Peatlands can be found in the arctic, boreal, temperate and tropical zones, and support a unique biodiversity in terms of plants, animals and microorganisms (bacteria, filamentous fungi and yeasts). Fungi are mainly responsible for the degradation of peat, as a result of their ability to degrade lignin. On the opposite, yeasts are involved in the utilization of simple carbon compounds and are generally considered secondary saprotrophs; however, their ecological roles in this ecosystem still need to be clarified (Thormann 2007, Juan-Ovejero et al. 2020). In recent years, investigations on yeasts as plant growth promoters (PGP) have significantly increased, stimulating studies on in yeasts isolated from this habitat (Jaiboon et al. 2017). The aim of this work was to isolate and identify yeasts from peat samples, and to screen them for PGP traits. Peat samples were collected from two alpine peatlands (Northen Italy) at different depths, diluted 1:10 and plated on YM agar supplemented with sodium propionate to inhibit filamentous fungi growth. A total of 12 strains were analyzed. Most of them belonged to taxa previously identified in peatland environments (e.g., Candida vartiovaarae). Conversely, Solicocczyma acquatica and Phaeotremella ovata were new records for this ecosystem. Furthermore, based on phylogenetic analysis, two isolates (Halobasidium sp. and Sterigmatospora sp.) could not be assigned to any recognized species. The PGP traits of strains were evaluated by screening for phosphate solubilization, ammonia production, indole-3-acetic acid (IAA) production, 1-aminocyclopropane-1-carboxylate (ACC) deaminase activity, and siderophore production. This study investigated, for the first time, the yeast biodiversity using culturable methods, and PGP traits of selected strains, suggesting their potential application as biofertilizers or regulators in sustainable agriculture.