Recent studies revealed a high diversity of fungal endophytes in traded tree seeds, including potential plant pathogens. The factors determining richness and composition of seed mycobiomes are poorly understood, but might be an important determinant for tree health. We assessed the relative impact of host identity, site, several site-specific environmental factors, and whether the host was sampled in its native or non-native distribution range, on the richness and composition of fungal seed endophytes of nine tree species across 15 sites in Europe and North America. Our results show that fungal richness was affected by host identity, but not by environmental variables or host distribution range. Fungal community composition was primarily driven by host identity, and to a lesser extent by environment. Around 25% of the 2147 amplicon sequence variants (ASVs) were generalists appearing on both continents and in both gymnosperms and angiosperms. Around 63% of the ASVs appeared in only gymnosperms or angiosperms, and 33% of the ASVs were associated with a single host species, while none were found in all tree species. Our results suggest that although seed trade might facilitate movements of fungi, their establishment and spread in the new environment might be limited by host availability.

中文翻译：

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树种子真菌内生菌的丰富性和群落组成的驱动因素。

最近的研究表明，交易的树木种子中真菌内生菌种类繁多，包括潜在的植物病原体。决定种子真菌生物素含量和组成的因素知之甚少，但可能是树木健康的重要决定因素。我们评估了宿主身份，位点，几个特定于位点的环境因素的相对影响，以及是否在其天然或非天然分布范围内采样宿主，对15个位点上9种树种的真菌种子内生菌的丰富度和组成在欧洲和北美。我们的结果表明，真菌丰富度受宿主身份的影响，但不受环境变量或宿主分布范围的影响。真菌群落组成主要由寄主身份驱动，在较小程度上受环境驱动。在2147个扩增子序列变体（ASV）中，大约有25％的人是遍及两大洲，裸子植物和被子植物的通才。大约63％的ASV仅出现在裸子植物或被子植物中，而33％的ASV与单个寄主物种相关，而在所有树种中均未发现。我们的结果表明，尽管种子贸易可能会促进真菌的迁移，但它们的建立和在新环境中的传播可能会受到寄主可用性的限制。