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。过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，若要更深入理解植物-真菌的关联模式，跨环境梯度的非生物与生物驱动因子的联合效应或许至关重要。
2. 本研究针对瑞士石松（Pinus cembra）关联真菌的发生与丰度，探究了温度、pH值、土壤含水量、植被覆盖度以及与宿主植物的距离对其的影响。研究采用DNA宏条形码（DNA metabarcoding）技术，对瑞士阿尔卑斯山区两个山谷中、覆盖瑞士石松当前海拔分布范围（1850~2250米a.s.l.）及以外区域的288份土壤样本进行了检测。我们构建了模型，分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（OTUs）的DNA读段丰度的影响。此外，我们还验证了非生物与生物因子是否会对不同宿主特异性类型的真菌（即泛宿主真菌、专性宿主真菌）产生差异化影响。
3. 研究发现，泛宿主真菌与专性宿主真菌的发生范围均超出了其宿主植物当前的海拔分布区间。非生物因子对所有真菌OTUs的丰度仅存在微弱影响。但我们观察到，宿主植物对一种专性宿主致病真菌的丰度存在正向影响，这为‘同种宿主植物附近病原菌富集的詹森-康奈尔效应（Janzen-Connell effect）’提供了支持。同时我们还发现，一种专性外生菌根真菌的丰度对宿主植物存在正向响应，这暗示存在‘反向’詹森-康奈尔效应。
4. 综合分析：本研究结果表明，负距离依赖效应不仅塑造了宿主专性真菌病原菌的分布，同样也影响了宿主专性真菌互利共生伙伴的分布。我们据此推断，致病型与互利型真菌在宿主植物当前海拔分布范围以外的发生情况，或将决定它们在未来气候变暖情景下的潜在分布范围迁移。