Climate change is altering tree species distributions, but these responses may vary among functional guilds. Temperate forest trees typically form associations with either arbuscular mycorrhizal (AM) fungi or ectomycorrhizal (EM) fungi. We predicted that tree seedlings would survive better in neighborhoods of their own guild, and that this positive feedback would be modified when seedlings are under drier conditions. Positive feedbacks may stem from higher abundance and diversity of symbionts, impacts on N cycling, and/or common networks for seedlings growing under adult trees of their own, versus mismatched, mycorrhizal guilds. To distinguish possible drivers, we tested whether feedbacks correlated with fungal community diversity and biochemical properties of soil.
We quantified the effects of mycorrhizal guild (EM vs. AM seedling success under EM vs. AM canopy trees) and drought conditions in a field experiment in central Illinois forest. We grew seedlings in a split-plot design, where we established 12 large plots with a gradient of AM and EM canopy tree basal area. In each block, were six subplots, where three were covered with throughfall rain reduction shelters, while the others had sham shelters. Each sub-plot had one each of eight tree species – four AM and four EM species. From each sub-plot, we characterized the diversity and composition of soil fungal communities and C:N ratios in soils, and correlated them to seedling survival.
Results/Conclusions
Seedlings showed relatively equal survivorship when growing in plots dominated a matched or mismatched mycorrhizal guild. However, in throughfall rain reduction subplots, seedlings in both mycorrhizal guilds significantly increased their survival when the canopy matched mycorrhizal guild. Correlation data suggests that positive feedbacks may stem from both higher mycorrhizal community diversity and altered C:N ratios in soils.
Climate change is expected to lead to dramatic changes to the species composition of forests. Unexpected resiliency may emerge at the level of mycorrhizal guilds. Understanding whether the dominant mycorrhizal guild of forests remains stable, independent of species level changes within guilds, may have important implications for future forest functioning.