Research ArticleECOLOGY

Shifts in dominant tree mycorrhizal associations in response to anthropogenic impacts

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Science Advances  10 Apr 2019:
Vol. 5, no. 4, eaav6358
DOI: 10.1126/sciadv.aav6358
  • Fig. 1 Distribution of forest tree mycorrhizal types and their associated factors in forests of the contiguous United States.

    (A) Geographical distribution of AM tree dominance. (B) Distribution of AM tree dominance in climatic space. MAP, mean annual precipitation; MAT, mean annual temperature. (C) Relative effects of MAP, MAT, and tree basal area on AM tree dominance. Each dot in (A) and (B) represents a plot and is colored on the basis of the associated AM-EM tree dominance. Boundaries of ecoregions (solid line) and nested subecoregions (dashed lines) in (A) are based on Cleland et al. (58). Circles in (B) indicate ecoregion-level mean MAT and MAP values with the associated SDs. The circle is colored on the basis of the mean AM tree dominance, and the size is proportional to the number of plots (log scale). Effects of MAP, MAT, and basal area on AM tree dominance across ecoregions in the contiguous United States (C) were tested using generalized mixed-effects models with subecoregions included as a random effect in each model. Significant coefficient estimates are plotted in (C) as solid circles, and nonsignificant ones are plotted as open circles. Circle size is proportional to the number of plots (log scale). The number beside each dot in (B) and (C) represents the associated ecoregion in (A). Error bars in (C) are SEs.

  • Fig. 2 Changes in forest AM tree dominance during the past three decades and the relative impacts of environmental changes on the mycorrhizal association changes in forests of the eastern United States.

    (A) Changes in AM tree dominance over the two inventories (T2-T1). All ecoregions had a significant increase in AM tree dominance during the period based on a paired Wilcoxon signed-rank test (P < 0.05; inset figures are boxplots of hexagon-level changes by ecoregions). (B) Relative effects of climate and basal area change, AM tree dominance at the first inventory (T1), N deposition, and fire frequency on AM tree dominance change. (C) Effects of tree abundance change of the top 10 most abundant tree genera (genera on the left without shaded background are AM trees, and genera on the right are EM trees) on AM tree dominance change. Mean coefficients in (B) and (C) were estimated at the ecoregion level based on generalized mixed-effects models with subecoregions included as a random effect. Significant coefficient estimates are plotted as solid circles, and nonsignificant ones are plotted as open circles with the size being proportional to the number of hexagons (log scale). Error bars in (B) and (C) are SEs.

  • Fig. 3 AM tree dominance differences between adult trees and saplings in forests across 11 ecoregions of the United States.

    The difference in AM tree dominance between adults and saplings for each ecological region were tested on the basis of a paired Wilcoxon signed-rank test (*P < 0.05; **P < 0.01; ***P < 0.001). Error bars are SEs. The bar thickness is proportional to the number of plots (log scale). Only plots where both adult trees and saplings are present are used for the analysis (98,638 plots).

  • Fig. 4 Associations between forest soil C and N with forest tree mycorrhizal type and environmental factors in forest ecosystems in the United States.

    (A to C) Relationships between AM tree dominance and soil (A) C stock, (B) N stock, and (C) C:N ratio (based on 0- to 20-cm depth mineral soil and litter layer). Linear regression lines were fitted by ecoregion (solid line, P < 0.05; dotted line, P > 0.05; red, positive slope; blue, negative slope). Inset shows coefficient (slope) estimate of the fitted line for each ecoregion (colored bars indicate significant relationship at P < 0.05; red, positive; blue, negative). (D to F) Effects of AM tree dominance and environmental factors on soil (D) C stock, (E) N stock, and (F) C:N ratio across ecoregions of the United States. Coefficient estimates in (D) to (F) are based on mixed-effect models at ecoregion level with subecoregions as a random effect. Significant coefficient estimates are plotted as solid circles, and nonsignificant ones are plotted as open circles. Circle size is proportional to the number of plots (log scale). Error bars are SEs. The number beside each bar in (A) to (C) and each dot in (D) to (F) represents the associated ecoregion in (A). Soil data summary is available in table S2.

Supplementary Materials

  • Supplementary material for this article is available at http://advances.sciencemag.org/cgi/content/full/5/4/eaav6358/DC1

    Fig. S1. Distribution of AM and EM forest trees in geographical and climatic space.

    Fig. S2. Spatial patterns of climatic factors (MAP and MAT change), basal area change, total N deposition (2000–2015), and fire frequency (1992–2015) used in the model in Fig. 2B.

    Fig. S3. Changes in AM and EM tree basal area in forests in eastern USA during the past three decades (T2-T1).

    Fig. S4. Effects of AM tree dominance and environmental factors on the 0- to 20-cm depth mineral soil C and N stocks and C:N ratio in forest ecosystems.

    Table S1. Vegetation and climate data summary used for tree mycorrhizal association distribution map in Fig. 1.

    Table S2. Soil data summary.

    Reference (58)

  • Supplementary Materials

    This PDF file includes:

    • Fig. S1. Distribution of AM and EM forest trees in geographical and climatic space.
    • Fig. S2. Spatial patterns of climatic factors (MAP and MAT change), basal area change, total N deposition (2000–2015), and fire frequency (1992–2015) used in the model in Fig. 2B.
    • Fig. S3. Changes in AM and EM tree basal area in forests in eastern USA during the past three decades (T2-T1).
    • Fig. S4. Effects of AM tree dominance and environmental factors on the 0- to 20-cm depth mineral soil C and N stocks and C:N ratio in forest ecosystems.
    • Table S1. Vegetation and climate data summary used for tree mycorrhizal association distribution map in Fig. 1.
    • Table S2. Soil data summary.
    • Reference (58)

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