Ectomycorrhizal (EcM) tree species often become more dominant than arbuscular mycorrhizal (AM) tree species in temperate forests, but they generally coexist. Theory predicts that ecological feedback mediated by aboveground herbivory and/or belowground microbes could explain these dominance/coexistence patterns. An experimental test of how aboveground/belowground organisms associated with AM/EcM trees mediate ecological feedbacks has been lacking at the community-level. By establishing AM and EcM tree sapling assemblages in mesocosms and then introducing seedlings of each type in a reciprocal planting experiment, we compared seedling performance under varying sapling species (conspecifics, heterospecifics within the same and different mycorrhizal types), using traits that reflect either aboveground herbivory-mediated feedback or belowground fungal-mediated feedback or both. When examining seedling traits that reflect aboveground herbivory-mediated feedbacks (i.e., foliar damage), AM plants tended to experience less foliar damage and EcM plants more damage under conspecific versus heterospecific saplings within the same mycorrhizal types, and aboveground herbivory-mediated feedback was species-specific rather than mycorrhizal type–specific. Conversely, when examining traits that reflect belowground fungal-mediated feedbacks, both AM and EcM plant species often exhibited mycorrhizal type-specific feedbacks (e.g., greater aboveground biomass under the same versus different mycorrhizal-type saplings) rather than species-specific feedbacks. Furthermore, tree species affected by herbivory-mediated feedback were less affected by belowground feedback, indicating that the relative importance of the feedbacks varied among plant species. Analysis of plant-associated organisms verified that the feedback outcomes corresponded with species accumulation of belowground fungi (but not of aboveground herbivores). Thus, aboveground herbivores drive stronger plant species-specific feedback than belowground fungi to regulate temperate tree diversity.

在温带森林中，外生菌根（EcM）树种通常比丛枝菌根（AM）树种更占优势，但它们通常共存。理论预测，地上食草动物和/或地下微生物介导的生态反馈可以解释这些优势/共存模式。在社区一级，缺乏与AM / EcM树相关的地上/地下生物如何介导生态反馈的实验测试。通过在中胚层中建立AM和EcM树苗组合，然后在对等种植实验中引入每种类型的幼苗，我们比较了不同树苗物种（相同和不同菌根类型内的同种异质种）的幼苗性能，使用反映地上食草动物介导的反馈或地下真菌介导的反馈或两者的特征。当检查能够反映地上食草植物介导的反馈（即叶面损害）的幼苗性状时，在相同菌根类型下，同种树苗与异种树苗相比，AM植物倾向于遭受较少的叶面损害，而EcM植物倾向于遭受更多的损害，并且地上食草植物介导的反馈是物种特定而非菌根类型特定。相反，当检查反映地下真菌介导的反馈的性状时，AM和EcM植物物种通常都表现出菌根类型的反馈（例如，相同和不同菌根类型的树苗下较高的地上生物量）而不是物种特异性的反馈。此外，食草动物介导的反馈影响的树种受地下反馈的影响较小，这表明反馈的相对重要性在植物物种之间有所不同。对植物相关生物的分析证实，反馈结果与地下真菌（而不是地下食草动物）的物种积累相对应。因此，地上食草动物比地上真菌能驱动更强的植物物种特异性反馈，从而调节温带树木的多样性。