The ideal‐weed hypothesis predicts that invasive plants should be less dependent on mutualisms. However, evidence in favor of or against this hypothesis comes mainly from observational studies. Here, we experimentally tested this hypothesis using a two‐factor greenhouse experiment, comparing the seedling growth response of different Pinus species (varying in invasiveness) to ectomycorrhizal fungal inoculation. Most species showed no response until they were 6 mo old, at which point inoculation increased growth between 10 and 260% among the different species. This growth response was higher for species with lower seed mass, higher dispersal ability, higher Z score (a proxy for invasiveness) and higher number of naturalized regions, all of which correspond to higher invasiveness. Our results show that timing is a crucial factor when comparing mycorrhizal dependency of different species. Dependence on mutualistic microorganisms could be part of a strategy in which invasive species produce smaller seeds, in greater number, which can disperse further, but where seedlings are more reliant on mycorrhizas to improve access to water, nutrients, and protection from pathogens. Our results suggest that reliance on mutualisms may enhance, rather than limit, nonnative species in their ability to spread, establish, and colonize.

中文翻译：

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入侵树木更多地依靠菌根，这与理想杂草假说相反

理想杂草假说预测，入侵植物应减少对共生的依赖。但是，支持或反对该假设的证据主要来自观察研究。在这里，我们使用两因素温室实验对这一假设进行了实验性测试，比较了不同松树种（侵袭性）对外生菌根真菌接种的幼苗生长反应。大多数物种直到6个月大时才显示出响应，此时接种增加了不同物种之间10％至260％的生长。对于具有较低种子质量，较高分散能力和较高Z的物种，该生长响应较高。得分（代表侵略性）和较高数量的归化区域，所有这些都对应于更高的侵略性。我们的结果表明，时机是比较不同物种的菌根依赖性的关键因素。依赖共生微生物可能是一种策略的一部分，在这种策略中，入侵物种产生的种子数量更多，种子数量更多，种子可以进一步分散，但幼苗更依赖菌根以改善对水，养分的获取，并免受病原体的侵害。我们的研究结果表明，对互惠主义的依赖可以增强而非限制外来物种的传播，建立和定居能力。