Dynamics of in situ growth and taxonomic structure of fungal communities in Alpine supraglacial debris

Supraglacial debris of Miage Glacier (Mont Blanc, Italy) was used as an in situ model for monitoring growth and modification of the taxonomic structure of fungal populations using an in-growth mesh bag approach over three consecutive years. Sterilized debris was placed in mesh bags (MB) and buried in the debris layer. Pristine debris (D) covering the surface of the glacier was also studied for comparative purposes. Quantitative PCR revealed that after a time of between one and two years the fungal abundance in the sterilized supraglacial debris contained in MB increased to reach a level comparable with those found in D samples. Likewise, the analysis of alpha-diversity exhibited similar dynamics during the three years of study. On the contrary, beta-diversity and Linear discriminant analysis Effect Size (LEfSe), showed apparently fluctuating dynamics from the first to the third year of study and a reduction of the number of fungal taxa discriminating MB and D samples. These observations confirm the hypothesis that fungal cells deposited on MB either by the surrounding debris or continuously brought via wind or atmospheric precipitations, can be subjected to an in situ growth which leads the abundance of the fungal communities occurring in MB to levels found in pristine debris (D) but showing fluctuating taxonomic structures.