Data from: Spatial patterns of pathogenic and mutualistic fungi across the elevational range of a host plant

1. Fungi are both agents of disease and mutualistic partners of plants. Previous studies have tested the effects of abiotic or biotic factors on plant-associated fungal communities in isolation. However, to better understand patterns of plant-fungal associations, the combined effects of abiotic and biotic drivers across environmental gradients may be important.
2. We investigated the effects of temperature, pH, soil moisture, vegetation cover and distance to host plant on the occurrence and abundance of fungi associated with Swiss stone pine (Pinus cembra). We did this by DNA metabarcoding 288 soil samples taken across and beyond the elevation range of P. cembra (i.e. 1850 – 2250 m a.s.l.) in two valleys in the Swiss Alps. We modeled the effects of abiotic and biotic factors on DNA read abundance of pathogenic and mutualistic fungal operational taxonomic units (OTUs) associated with P. cembra. We also tested whether abiotic and biotic factors differentially affected fungi of varying host specificity (i.e. host generalists, host specialists).
3. We found that the occurrences of both host generalist and specialist fungi exceeded the current elevational range of their host plant. Abiotic factors had only minor effects on the abundances of all fungal OTUs. However, we found positive effects of the host plant on the abundance of a host specialist pathogenic fungus, providing support for a Janzen-Connell effect of high pathogen accumulation close to conspecific host plants. We also found a positive response to the host plant in a specialist ectomycorrhizal fungus, suggesting an “inverse” Janzen-Connell effect.
4. Synthesis. Our findings imply that negative distance dependence shapes not only the distribution of host-specific fungal pathogens, but also host-specific fungal mutualists. We conclude that the occurrence of both pathogenic and mutualistic fungi beyond the current elevational range of host plants may determine their potential range shifts under projected climate warming.

1. 真菌既是植物病害的致病菌，也是植物的互利共生伙伴。既往研究多单独探究非生物或生物因子对植物关联真菌群落的影响。然而，为更深入阐明植物-真菌共生模式的形成机制，探究环境梯度下非生物与生物驱动因子的联合效应具有重要意义。
2. 本研究以瑞士阿尔卑斯山区两个山谷内的瑞士石松（*Pinus cembra*）为研究对象，采集其现有海拔分布范围（1850~2250 m 海拔以上）及分布范围外的288份土壤样本，通过DNA宏条形码（DNA metabarcoding）技术，分析温度、pH值、土壤含水量、植被覆盖度以及与寄主植物的距离对其关联真菌的发生频率与丰度的影响。本研究构建了模型以解析非生物与生物因子对与瑞士石松关联的致病型、互利型真菌操作分类单元（operational taxonomic units, OTUs）的DNA读取丰度的调控作用；同时验证了非生物与生物因子对不同寄主专化性真菌（即广寄主真菌、专化寄主真菌）的影响是否存在差异。
3. 研究结果显示，广寄主与专化寄主真菌的发生范围均超出了其寄主植物当前的海拔分布区间。非生物因子对所有真菌OTUs的丰度仅存在微弱调控作用。然而，我们发现寄主植物对专化寄主致病真菌的丰度具有显著正向效应，这为「同种寄主植物附近病原菌富集的詹森-康奈尔（Janzen-Connell）效应」提供了实证支持；同时，专化寄主外生菌根真菌的丰度也对寄主植物呈现正向响应，这暗示了一种「反向詹森-康奈尔效应」。
4. 综合与结论：本研究结果表明，负距离依赖效应不仅调控寄主专化性真菌病原菌的分布，同时也影响寄主专化性真菌共生伙伴的分布格局。我们认为，致病型与互利型真菌在寄主植物当前海拔分布范围外的发生情况，将决定其在未来气候变暖情景下的潜在分布范围迁移潜力。