In temperate and boreal forests, competition for soil resources between free-living saprotrophs and ectomycorrhizal (EcM) fungi has been suggested to restrict saprotrophic fungal dominance to the most superficial organic soil horizons in forests dominated by EcM trees. By contrast, lower niche overlap with arbuscular mycorrhizal (AM) fungi could allow fungal saprotrophs to maintain this dominance into deeper soil horizons in AM-dominated forests. Here we used a natural gradient of adjacent forest patches that were dominated by either AM or EcM trees, or a mixture of both to determine how fungal communities characterized with high-throughput amplicon sequencing change across organic and mineral soil horizons. We found a general shift from saprotrophic to mycorrhizal fungal dominance with increasing soil depth in all forest mycorrhizal types, especially in organic horizons. Vertical changes in soil chemistry, including pH, organic matter, exchangeable cations, and extractable phosphorus, coincided with shifts in fungal community composition. Although fungal communities and soil chemistry differed among adjacent forest mycorrhizal types, variations were stronger within a given soil profile, pointing to the importance of considering horizons when characterizing soil fungal communities. Our results also suggest that in temperate forests, vertical shifts from saprotrophic to mycorrhizal fungi within organic and mineral horizons occur similarly in both ectomycorrhizal and arbuscular mycorrhizal forests.

在温带和寒带森林中，自由生活的腐生菌和外生菌根 (EcM) 真菌之间对土壤资源的竞争已被建议将腐生真菌的优势限制在以 EcM 树木为主的森林中最表层的有机土壤层。相比之下，与丛枝菌根 (AM) 真菌较低的生态位重叠可以使真菌腐生菌在 AM 主导的森林中保持这种优势进入更深的土壤层。在这里，我们使用由 AM 或 EcM 树或两者的混合物主导的相邻森林斑块的自然梯度来确定真菌群落如何以高通量扩增子测序为特征，跨越有机和矿物土壤层。我们发现随着所有森林菌根类型土壤深度的增加，真菌从腐生到菌根的优势普遍转变，尤其是在有机视野中。土壤化学的垂直变化，包括 pH 值、有机质、可交换阳离子和可提取磷，与真菌群落组成的变化同时发生。尽管相邻森林菌根类型的真菌群落和土壤化学不同，但在给定的土壤剖面内变化更大，这表明在表征土壤真菌群落时考虑视野的重要性。我们的研究结果还表明，在温带森林中，在外生菌根和丛枝菌根森林中，有机和矿物范围内从腐生真菌到菌根真菌的垂直转变类似。恰逢真菌群落组成的变化。尽管相邻森林菌根类型的真菌群落和土壤化学不同，但在给定的土壤剖面内变化更大，这表明在表征土壤真菌群落时考虑视野的重要性。我们的研究结果还表明，在温带森林中，在外生菌根和丛枝菌根森林中，有机和矿物范围内从腐生真菌到菌根真菌的垂直转变类似。恰逢真菌群落组成的变化。尽管相邻森林菌根类型的真菌群落和土壤化学不同，但在给定的土壤剖面内变化更大，这表明在表征土壤真菌群落时考虑视野的重要性。我们的研究结果还表明，在温带森林中，在外生菌根和丛枝菌根森林中，有机和矿物范围内从腐生真菌到菌根真菌的垂直转变类似。