Ectomycorrhizal fungal communities of Swiss stone pine (Pinus cembra) depend on climate and tree age in natural forests of the Alps

Abstract

Background and aims: Pinus cembra represent a typical and important tree species growing in European subalpine and alpine habitats. The ectomycorrhizal (ECM) fungal communities associated to this tree under natural conditions are largely unknown.

Methods: In this study, we investigated the ECM fungal abundance and composition at four high-altitude sites (two northern-exposed and two southern-exposed habitats) in South Tyrol (Italy), and included also two different age classes of P. cembra. The ECM partners were characterized morphologically, and identified by rDNA ITS sequence analysis.

Results: The degree of mycorrhization in adult P. cembra was typically 100% in these natural habitats, with a total species diversity of 20 ECM species. The four high-altitude sites were similar concerning their species richness and mycobiont diversity, but they differed significantly in ECM species composition. Young P. cembra had a mycorrhization degree of 100% and a total of 10 species were observed. All mycorrhizal partners of naturally regenerated young P. cembra were only detected in one specific location, with the exception of Cenococcum sp. and Amphinema sp. which were detected at two sites. Young trees harbour a distinct ectomycorrhizal fungal diversity, which is clearly lower than the diversity detected in adult P. cembra trees. The P. cembra bolete (Suillus plorans) is the most important symbiotic partner of P. cembra at Southern Tyrolean high-altitude sites and is known for its strict, species-specific host association.

Conclusions: The ectomycorrhizal fungal community composition strongly depends on geographic region and on the slope exposure (north or south) of the site.

Supplementary information: The online version contains supplementary material available at 10.1007/s11104-022-05497-z.

Keywords: Alpine timberline ecotone; Cool and dry forests; Rhizopogon; Slope exposure; Suillus.

Fig. 1

a Southern Tyrolean study region including the four sampling sites for the investigation of the ECM communities of Pinus cembra. The sampling sites are marked: Pustertal southern-exposed Ahornach—dark brown; Pustertal northern-exposed Weißenbach—light brown; Vinschgau southern-exposed Kortsch -purple; Vinschgau northern-exposed Latzaun—light purple. The slope area of the sites is also marked on the map. b P. cembra trees of different age stages investigated during this study: adult individuals (left) and young individuals (right—arrow)

Fig. 2

Nonmetric multidimensional scaling (NMDS) analysis based on Adonis and Bray–Curtis distance matrix on the OTUs sequences of the ECM fungal community in different Pinus cembra sites. Stress value = 0.0289. Total R² = 0.681. Points closer together in the ordination space have more similar community assemblages

Fig. 3

Relative abundance of ECM fungi at the species level compared between adult and young P. cembra trees in the different sampling regions (Pustertal, Vinschgau) and sites (representing the slope exposure north, south)

Fig. 4

Differential representation of significantly abundant ECM taxa found in the P. cembra roots of adult (above) and young (below) Pinus cembra trees. On the x axis, ECM species are ordered based on their overall abundances across all four sites. For each species, dots represent their relative abundance (%) coloured by region (Pustertal or Vinschgau), and labelled by site (representing slope exposure north or south). Taxa found in both the adult and young trees are underlined

Fig. 5

Heatmap and accompanying cluster analysis (x axis) of the relative occurring frequency of ECM fungal taxa across Pinus cembra of the same site (regions: Pustertal, Vinschgau; face: north, south) and age stage (adult, young). The occurrence frequency for each taxon across sampled trees is coloured in the shades of light yellow (low frequency) to red (high frequency). The number of times each taxon was detected across replicates is given by the frequency percentage, spanning from 100%, taxa detected in all the replicates, to 0%, taxa never detected