Patterns of diversity, endemism and specialization in the root symbiont communities of alder species on the island of Corsica

We investigated whether the diversity, endemicity and specificity of alder symbionts could be changed by isolation in a Mediterranean glacial refugium. We studied both ectomycorrhizal (EM) fungi and nitrogen-fixing actinobacteria associated with alders, and compared their communities in Corsica and on the European continent. Nodules and root tips were sampled on the three alder species present in Corsica and continental France and Italy. Phylogenies based on internal transcribed spacer (ITS) and a multilocus sequence analysis approach were used to characterize fungal and Frankia species, respectively. Patterns of diversity, endemism and specialization were compared between hosts and regions for each symbiont community. In Corsica, communities were not generally richer than on the mainland. The species richness per site depended mainly on host identity: Alnus glutinosa and Alnus cordata hosted richer Frankia and EM communities, respectively. Half of the Frankia species were endemic to Corsica against only 4% of EM species. Corsica is not a hotspot of diversity for all alder symbionts but sustains an increased frequency of poor-dispersers such as hypogeous fungi. Generalist EM fungi and host-dependent profusely sporulating (Sp+) Frankia were abundantly associated with Corsican A. cordata, a pattern related to a more thermophilic and xerophylic climate and to the co-occurrence with other host trees.

Ectomycorrhizal and endophytic fungi associated with Alnus glutinosa growing in a saline area of central Poland

Alnus glutinosa (black alder) is a mycorrhizal pioneer tree species with tolerance to high concentrations of salt in the soil and can therefore be considered to be an important tree for the regeneration of forests areas devastated by excessive salt. However, there is still a lack of information about the ectomycorrhizal fungi (EMF) associated with mature individuals of A. glutinosa growing in natural saline conditions. The main objective of this study was to test the effect of soil salinity and other physicochemical parameters on root tips colonized by EMF, as well as on the species richness and diversity of an EMF community associated with A. glutinosa growing in natural conditions. We identified a significant effect of soil salinity (expressed as electrical conductivity: EC_e and EC_1:5) on fungal taxa but not on the total level of EM fungal colonization on roots. Increasing soil salinity promoted dark-coloured EMF belonging to the order Thelephorales (Tomentella sp. and Thelephora sp.). These fungi are also commonly found in soils polluted with heavy-metal. The ability of these fungi to grow in contaminated soil may be due to the presence of melanine, a natural dark pigment and common wall component of the Thelephoraceae that is known to act as a protective interface between fungal metabolism and biotic and abiotic environmental stressors. Moreover, increased colonization of fungi belonging to the class of Leotiomycetes and Sordiomycetes, known as endophytic fungal species, was observed at the test sites, that contained a larger content of total phosphorus. This observation confirms the ability of commonly known endophytic fungi to form ectomycorrhizal structures on the roots of A. glutinosa under saline stress conditions.