DOI: 10.5061/dryad.76hdr7t2c
title: Data from: A common ericoid shrub modulates the diversity and structure of fungal communities across an arbuscular to ectomycorrhizal tree dominance gradient

description: Differences between arbuscular (AM) and ectomycorrhizal (EcM) trees
 strongly influence forest ecosystem processes, in part through their
 impact on saprotrophic fungal communities. Ericoid mycorrhizal (ErM)
 shrubs likely also impact saprotrophic communities given that they can
 shape nutrient cycling by slowing decomposition rates and intensifying
 nitrogen limitation. We investigated the depth distributions of
 saprotrophic and EcM fungal communities in paired subplots with and
 without a common understory ErM shrub, mountain laurel (Kalmia latifolia
 L.), across an AM to EcM tree dominance gradient in a temperate forest by
 analyzing soils from the organic, upper mineral (0–10 cm), and lower
 mineral (cumulative depth of 30 cm) horizons. The presence of K. latifolia
 was strongly associated with the taxonomic and functional composition of
 saprotrophic and EcM communities. Saprotrophic richness was consistently
 lower in the Oa horizon when this ErM shrub species was present. However,
 in AM tree-dominated plots, the presence of the ErM shrub was associated
 with a higher relative abundance of saprotrophs. Given that EcM trees
 suppress both the diversity and relative abundance of saprotrophic
 communities, our results suggest that separate consideration of ErM shrubs
 and EcM trees may be necessary when assessing the impacts of plant
 mycorrhizal associations on belowground communities.
description: We carried out this study in the northeastern United States at
 Yale-Myers Forest (41°57’ N, 72°07’ W), which is characterized as
 temperate deciduous forest with a mean annual precipitation of 133 cm, a
 mean January temperature of -4.6°C, and mean July temperature of 21.7°C.
 The three forest stands used in this study are situated on glacial origin
 inceptisols from the Nipmuck-Brookfield complex and Woodbridge series,
 which consist of generally fine sandy loam soils (National Resources
 Conservation Service [NRCS], 2023). Elevations within sites ranged from
 180-290 m and the mean plot slope was 9 degrees (range 0.5-26; CT ECO,
 2016). The mean organic soil pH was 4.28 (range 3.16 -5.34) and mean
 mineral soil was 4.43 (range 2.78-5.48). Overall, the forest understory at
 our study site had a patchy distribution of the ErM shrub *K. latifolia*,
 which is the most abundant understory plant species at the forest and
 accounts for about one-third of all understory vegetation cover (Ward et
 al. 2021). In the organic horizon, carbon (C), and nitrogen (N) stocks
 were generally higher in plots with *K. latifolia*. In the surface mineral
 horizon (0-15 cm), soil C and N stocks were negatively associated with the
 percentage of EcM trees relative to AM trees (Ward *et al.*, 2023). ErM
 plant species other than *K. latifolia *make up a small percentage of
 understory plant cover at our forest site (&lt;2%; Ward et al. 2021),
 so we limited our study to *K. latifolia *since it was consistently
 present under both AM and EcM tree associations within each of the three
 stands.   We set up six
 plots within the three forest stands that each included paired 1-m radius
 subplots with and without *K. latifolia* (n= 36 total). Subplots were ~2 m
 apart with one under *K. latifolia* and the other in open understory
 habitat with no shrub layer. This orthogonal design ensured that there was
 no correlation between tree mycorrhizal association and the absence or
 presence of *K. latifolia*, permitting the ErM shrub effect to be
 disentangled from the effects of tree mycorrhizal associations. We
 identified and measured diameter at breast height (DBH; 1.37 m height) of
 all trees ≥20 cm DBH within 10 m of plot center, ≥5 cm DBH within 5 m of
 plot center, and 1-5 cm DBH within 1 m of each subplot center (i.e. the
 nested subplots with or without *K. latifolia*). We calculated the basal
 area of each tree species in m2 ha-1, assigned mycorrhizal associations to
 each tree genus based on the designations in Soudzilovskaia et al. (2020),
 and calculated canopy tree mycorrhizal dominance in each plot as the
 percentage of EcM tree basal area out of total basal area. This study
 design resulted in plots that ranged from 0 to 97% EcM tree basal
 area.   Soil sampling was
 carried out in June 2021. In each subplot (*n* = 36), we collected soil
 samples from three depths: the organic horizon (Oa; Fig. 1, left panel),
 surface mineral horizon (0-10 cm of mineral horizon; Fig. 1, top right
 panel), and subsurface mineral horizon (beginning from a depth of 10 cm in
 the mineral horizon to a cumulative depth, including the Oa, of 30 cm;
 Fig. 1, bottom left panel). We sampled the Oa horizon by first removing
 plant litter and then pooling two 25 x 25 cm areas of Oa. For the mineral
 horizons, we pooled two cores from each depth using a 5-cm diameter soil
 corer. Out of a total of 108 subplot and depth samples, two subplots did
 not have an Oa horizon, resulting in a total of 106 soil samples. Soils
 from each subplot at the three soil depths were passed through a 4-mm
 sieve. A 5-g subsample of soil was placed in a sterile Whirl-Pak bag which
 was frozen at -20°C until DNA extraction. Soil pH was measured on fresh
 soil using a 1:1 volumetric soil to deionized water ratio and a benchtop
 pH probe. Gravimetric soil moisture was measured from fresh soil by oven
 drying soils at 105°C for 24 h.
description: # Data from: A common ericoid shrub modulates the diversity and structure
 of fungal communities across an arbuscular to ectomycorrhizal tree
 dominance gradient
 [https://doi.org/10.5061/dryad.76hdr7t2c](https://doi.org/10.5061/dryad.76hdr7t2c) Includes dataset: ErM_dataDryad.csv Metadata file with variable (column) descriptions: ErM_dataDryad_metadata.csv NA values in data are missing values.