Insect outbreaks of increasing frequency and severity in forests are predicted due to climate change. Insect herbivory is known to promote physiological changes in forest trees. However, little is known about whether these plant phenotypic adjustments have cascading effects on tree microbial symbionts such as fungi in roots and foliage. We studied the impact of defoliation by the pine processionary moth in two infested Pinus nigra forests through a multilevel sampling of defoliated and non-defoliated trees. We measured tree growth, nutritional status and carbon allocation to chemical defenses. Simultaneously, we analyzed the putative impact of defoliation on the needle endophytes and on the soil fungal communities. Higher concentrations of chemical defenses were found in defoliated trees, likely as a response to defoliation; however, no differences in non-structural carbohydrate reserves were found. In parallel to the reductions in tree growth and changes in chemical defenses, we observed shifts in the composition of needle endophytic and soil fungal communities in defoliated trees. Defoliated trees consistently corresponded with a lower biomass of ectomycorrhizal fungi in both sites, and a higher alpha diversity and greater relative abundance of belowground saprotrophs and pathogens. However, ectomycorrhizal alpha diversity was similar between non-defoliated and defoliated trees. Specific needle endophytes in old needles were strongly associated with non-defoliated trees. The potential role of these endophytic fungi in pine resistance should be further investigated. Our study suggests that lower biomass of ectomycorrhizal fungi in defoliated trees might slow down tree recovery since fungal shifts might affect tree-mycorrhizal feedbacks and can potentially influence carbon and nitrogen cycling in forest soils.

中文翻译：

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昆虫的脱叶与土壤外生菌根生物量的减少和针状内生群落的转移有关。

据预测，由于气候变化，森林中的昆虫暴发频率和严重性将增加。众所周知，食草昆虫可促进林木的生理变化。但是，对于这些植物的表型调节是否对树木的微生物共生体（如根和叶的真菌）具有连锁效应，人们所知甚少。我们研究了两个侵染的黑松中松树前进蛾对落叶的影响通过对落叶树和非落叶树进行多级采样来获取森林。我们测量了树木的生长，营养状况以及碳在化学防御中的分配。同时，我们分析了落叶对针状内生菌和土壤真菌群落的假定影响。在落叶树中发现了更高浓度的化学防御素，这可能是对落叶的一种反应。然而，未发现非结构性碳水化合物储量的差异。在树木生长减少和化学防御变化的同时，我们观察了落叶树中针状内生和土壤真菌群落组成的变化。在这两个地点，落叶树始终与较低的外生菌根真菌生物量相对应，地下腐生菌和病原体具有更高的α多样性和相对丰度。但是，未落叶树和落叶树之间的外生菌根α多样性相似。老针中的特定针内生菌与非落叶树密切相关。这些内生真菌在抗松中的潜在作用应进一步研究。我们的研究表明，落叶树中外生菌根真菌的生物量较低可能会减慢树木的恢复，因为真菌的转移可能会影响树木的菌根反馈，并可能影响森林土壤中的碳和氮循环。这些内生真菌在抗松中的潜在作用应进一步研究。我们的研究表明，落叶树中外生菌根真菌的生物量较低可能会减慢树木的恢复，因为真菌的转移可能会影响树木的菌根反馈，并可能影响森林土壤中的碳和氮循环。这些内生真菌在抗松中的潜在作用应进一步研究。我们的研究表明，落叶树中外生菌根真菌的生物量较低可能会减慢树木的恢复，因为真菌的转移可能会影响树木的菌根反馈，并可能影响森林土壤中的碳和氮循环。