Aims

The few remaining old-growth forests in the northeastern United States are often comprised of ectomycorrhizal (EM) tree-dominated patches surrounded by arbuscular mycorrhizal (AM) tree-dominated secondary forests. We examined how (1) distance from old growth and tree neighborhood composition influenced EM colonization, fungal richness, and fungal community composition of Betula lenta L. (black birch) seedlings, a common EM tree that colonizes abandoned agricultural fields, and (2) potential effects of EM fungal genera on seedling physiological performance.

Methods

We sampled soils and tree composition from the edge of an EM-dominated old-growth forest into an adjacent AM-dominated secondary forest. We used soils to grow black birch seedlings in a growth chamber bioassay. We measured seedling EM colonization and investigated effects of EM fungi and soil characteristics on seedling physiological performance.

Results

We identified 20 EM fungal species and found decreases in EM colonization and fungal richness with distance from old growth, with many taxa present only near the edge. Neighborhood EM tree abundance best explained EM colonization while distance interacted with EM tree basal area to best explain EM fungal richness of seedlings. Soils from neighborhoods lacking EM trees resulted in sparse EM colonization of seedlings. We found no clear effects of EM fungal genera on seedling performance, but we detected a slight decrease in seedling photosynthetic rate with distance from old growth.

Conclusions

Old-growth forests can be reservoirs of EM fungi, and EM tree patches can function as localized inoculum sources in AM-dominated secondary forests, potentially facilitating EM tree establishment.

中文翻译：

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靠近古老的森林边缘和外生菌根树岛增强了次生林土壤中黑桦幼苗的外生菌根真菌定殖

目标

美国东北部仅存的少数原始森林通常由外生菌根 (EM) 树为主的斑块组成，周围环绕着丛枝菌根 (AM) 树为主的次生林。我们研究了 (1) 距老树的距离和树木邻域组成如何影响黑桦树苗的 EM 定殖、真菌丰富度和真菌群落组成，黑桦树苗是一种常见的 EM 树，在废弃农田中定殖，以及 (2) EM真菌属对幼苗生理性能的潜在影响。

方法

我们从以 EM 为主的原始森林边缘到邻近的以 AM 为主的次生林中采样了土壤和树木成分。我们使用土壤在生长室生物测定中种植黑桦树苗。我们测量了幼苗的 EM 定植情况，并研究了 EM 真菌和土壤特性对幼苗生理性能的影响。

结果

我们鉴定了 20 种 EM 真菌物种，发现 EM 定殖和真菌丰富度随着距老生长距离的增加而减少，许多类群仅存在于边缘附近。邻近的 EM 树丰度最能解释 EM 定植，而距离与 EM 树断面积的相互作用最能解释幼苗的 EM 真菌丰富度。缺乏 EM 树的社区的土壤导致 EM 幼苗定植稀疏。我们发现 EM 真菌属对幼苗性能没有明显影响，但我们检测到幼苗光合速率随着远离老生长而略有下降。

结论

古老的森林可以成为 EM 真菌的储存库，而 EM 树斑块可以作为 AM 主导的次生林中的局部接种源，有可能促进 EM 树的建立。