High Fungal Diversity but Low Seasonal Dynamics and Ectomycorrhizal Abundance in a Mountain Beech Forest

Abstract

Forests on steep slopes constitute a significant proportion of European mountain areas and are important as production and protection forests. This study describes the soil fungal community structure in a European beech-dominated mountain forest stands in the Northern Calcareous Alps and investigates how it is determined by season and soil properties. Samples were collected at high spatial resolution in an area of ca. 100 m × 700 m in May (spring) and August (summer). Illumina MiSeq high-throughput sequencing of the ITS2-region revealed distinct patterns for the soil fungal communities. In contrast to other studies from temperate European beech forest stands, Ascomycota dominated the highly diverse fungal community, while ectomycorrhizal fungi were of lower abundance. Russulaceae, which are often among the dominant ectomycorrhizal fungi associated with European beech, were absent from all samples. Potentially plant pathogenic fungi were more prevalent than previously reported. Only subtle seasonal differences were found between fungal communities in spring and summer. Especially, dominant saprotrophic taxa were largely unaffected by season, while slightly stronger effects were observed for ectomycorrhizal fungi. Soil characteristics like pH and organic carbon content, on the other hand, strongly shaped abundant taxa among the saprotrophic fungal community.

Keywords: Ectomycorrhiza; Mountainous beech forest; Plant pathogenic fungi; Saprotrophic fungi; Soil fungal communities; Spatial and seasonal diversity.

Fig. 1

Relative abundance of fungal phyla (a) and ecological guilds (b) in May (green; spring) and August 2015 (yellow; summer) at the Molln site. A: Ascomycota; B: Basidiomycota; M: Mortierellomycota and Mucoromycota; phyla <1% are not displayed (see Online Resource 2, Table S2 for a list of OTUs). SAP, saprotrophic fungi; SYM, symbiotic fungi; PAT, potentially plant pathogenic fungi; NA, fungal guild not assigned

Fig. 2

Relative abundance of fungal families in the three different ecological groups in May (spring) and August (summer) 2015 at the Molln site. a SAP, saprotrophs; b SYM, symbionts (mainly ECM and sebacinalean root interactions [63]); c PAT, potentially plant pathogenic fungi. Ascomycota are colored in blue, Basidiomycota in red, Mucoromycota and Mortierellomycota in black/grey, and Chytridiomycota in yellow

Fig. 3

Seasonal changes in fungal community composition at the Molln site. PCoA of log-transformed UniFrac distances (green: May (spring) 2015; yellow: August (summer) 2015) of the total fungal community, TOT (a); the saprotrophic fungi, SAP (b); the symbiotic fungi, SYM (c); and the potentially plant pathogenic fungi, PAT (d). For scaling of grids, see d value in the upper right corner of each subpanel

Fig. 4

Seasonal responses of selected taxa of mycorrhizal fungi at the Molln site. Hygrophorus spp. (i.e., OTU_96 and 125) (a), Hyaloscyphaceae (i.e., OTU_11 and 27) (b), and Sebacinales (26 different OTUs) (c). Data are shown for the relative abundance in the total fungal community (TOT) and in the subset of symbiotic (SYM) fungi in May (green; spring) and August 2015 (yellow; summer). Please note the different scales of y-axes

Fig. 5

Environmental influences on fungal β-diversity at the Molln site. a Indices of β-diversity, Morisita-Horn (MH, blue), Bray-Curtis (BC, red), and UniFrac (UF, grey), were calculated from the fungal community data and plotted against the environmental distance. b BC β-diversity of symbiotic (SYM, green), saprotrophic (SAP, orange), and potentially plant pathogenic (PAT, purple) fungal guilds. Regression coefficients (r²) and significance levels (p < 0.001) are shown in corresponding colors

Fig. 6

Relative abundances (%) of selected fungal taxa in response to soil pH (a, d, g), soil organic C content (C_org) (b, e, h), and both factors (c, f, i) at the Molln site. Samples from May (green; spring) and August 2015 (yellow; summer) are shown separately. Where meaningful, regression lines were drawn (a Leotiomycetes i.s. pH, exponential; b Leotiomycetes i.s. C_org, polynomial; d Saitozyma podzolica OTU 6, exponential; g Mortierella sel. pH, linear; all shown correlations are highly significant at p < 0.001). In the response diagrams of fungal taxa to both pH and C_org (c, f, i), the relative abundance is pictured by the diameter of the circles. The largest circles indicate 29.7% relative abundance for Leotiomycetes i.s. (c), 16.6% for Saitozyma podzolica OTU 6 (f), and 13.9% for Mortierella sel. (i)