• Emergent diseases are an increasing problem in forests worldwide. Exotic pathogens are now threatening forests where pathogens have not traditionally been considered to be major ecological drivers of tree demography, such as water‐limited Mediterranean forests. However, how pathogens might limit regeneration in invaded forests is largely unknown.
• Here we used fungicide to analyse the impact of soil‐borne oomycete pathogens on seedling establishment at community level in Mediterranean forests invaded by the exotic oomycete Phytophthora cinnamomi . Fungicide effects were modelled as a function of the tree neighbourhood composition, the seed mass of the target species, and the abiotic environment.
• Fungicide application had positive effects on seedling performance that varied in magnitude and spatial structure among coexisting species. Seed mass predicted fungicide effects on seedling emergence, but not on survival or growth. Positive fungicide effects were modulated by levels of abiotic resources, mainly water, increasing with soil moisture.
• Our results support a novel role for soil‐borne oomycete pathogens as one more axis of the regeneration niche of woody species in water‐limited forests. Given the increasing numbers of exotic oomycete pathogens worldwide, more research is needed to understand the role of this relevant microbial group as a factor shaping seedling establishment.

中文翻译：

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土壤传播的病原体是地中海森林群落水平更新方式的决定因素

• 紧急疾病是全世界森林中日益严重的问题。现在，外来病原体正在威胁那些原本不认为病原体是树木人口统计学的主要生态驱动力的森林，例如地中海限水森林。然而，病原体如何限制被入侵森林的再生尚不清楚。
• 在这里，我们使用杀菌剂来分析土壤传播的卵菌病原体对外来卵菌的疫霉菌Pytophthora cinnamomi入侵的地中海森林社区水平上幼苗建立的影响。根据树木邻里组成，目标物种的种子质量和非生物环境对杀菌剂作用进行建模。
• 杀菌剂的使用对幼苗的生长有积极的影响，在共存物种中，其数量和空间结构各不相同。种子量预测了杀菌剂对幼苗出苗的影响，但对存活或生长没有影响。杀菌剂的积极作用受到非生物资源（主要是水）水平的调节，并随土壤湿度的增加而增加。
• 我们的结果支持土壤传播的卵菌病原体在水有限的森林中作为木本物种再生位的又一轴的新作用。鉴于世界范围内外来卵菌病原体的数量不断增加，需要更多的研究来了解这一相关微生物群作为影响幼苗生长的因素。