Abstract Research aimed at understanding the mechanisms underlying the relationship between tree diversity and antagonist infestation is often neglecting resource-use complementarity among plant species. We investigated the effects of tree species identity, species richness, and mycorrhizal type on leaf herbivory and pathogen infestation. We used a tree sapling experiment manipulating the two most common mycorrhizal types, arbuscular mycorrhiza and ectomycorrhiza, via respective tree species in monocultures and two-species mixtures. We visually assessed leaf herbivory and pathogen infestation rates, and measured concentrations of a suite of plant metabolites (amino acids, sugars, and phenolics), leaf elemental concentrations (carbon, nitrogen, and phosphorus), and tree biomass. Tree species and mycorrhizal richness had no significant effect on herbivory and pathogen infestation, whereas species identity and mycorrhizal type had. Damage rates were higher in arbuscular mycorrhizal (AM) than in ectomycorrhizal (EM) trees. Our structural equation model (SEM) indicated that elemental, but not metabolite concentrations, determined herbivory and pathogen infestation, suggesting that the investigated chemical defence strategies may not have been involved in the effects found in our study with tree saplings. Other chemical and physical defence strategies as well as species identity as its determinant may have played a more crucial role in the studied saplings. Furthermore, the SEM indicated a direct positive effect of AM trees on herbivory rates, suggesting that other dominant mechanisms, not considered here, were involved as well. We found differences in the attribution of elemental concentrations between the two rates. This points to the fact that herbivory and pathogen infestation are driven by distinct mechanisms. Our study highlights the importance of biotic contexts for understanding the mechanisms underlying the effects of biodiversity on tree-antagonist interactions.

中文翻译：

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营养状况而不是次生代谢物驱使食草动物和病原体侵染不同菌根的树木单一栽培和混合物

摘要 旨在了解树木多样性与拮抗剂侵染之间关系的潜在机制的研究往往忽视植物物种之间的资源利用互补性。我们研究了树种特性、物种丰富度和菌根类型对叶食草性和病原体侵染的影响。我们使用了树苗实验，通过单一栽培和两种混合物中的各自树种来操纵两种最常见的菌根类型，丛枝菌根和外生菌根。我们目视评估了叶食草和病原体侵染率，并测量了一系列植物代谢物（氨基酸、糖和酚类物质）的浓度、叶元素浓度（碳、氮和磷）和树木生物量。树种和菌根丰富度对食草动物和病原体侵染没有显着影响，而物种身份和菌根类型则有显着影响。丛枝菌根 (AM) 的损伤率高于外生菌根 (EM) 树。我们的结构方程模型 (SEM) 表明，元素而不是代谢物浓度决定了食草动物和病原体的侵染，这表明所研究的化学防御策略可能未涉及我们对树苗的研究中发现的影响。其他化学和物理防御策略以及物种身份作为其决定因素可能在所研究的树苗中发挥了更重要的作用。此外，SEM 表明 AM 树对食草率有直接的积极影响，这表明此处未考虑的其他主要机制，也参与其中。我们发现两种速率之间元素浓度的归因存在差异。这表明食草动物和病原体感染是由不同的机制驱动的。我们的研究强调了生物环境对于理解生物多样性对树木-拮抗剂相互作用影响的机制的重要性。