High throughput sequencing combined with null model tests reveals specific plant-fungi associations linked to seedling establishment and survival

1. Plant-fungal interactions are important for plant community assembly, but quantifying these relationships remains challenging. High throughput sequencing of fungal communities allows us to identify plant-fungal associations at a high level of resolution, but often fails to provide information on taxonomic and functional assignment of fungi.
2. We transplanted seeds of Pinus cembra across an elevational gradient (1850-2250 m a.s.l.) and identified environmental factors and known fungal associates important for seedling establishment and survival. We then applied null model tests to identify taxonomically unassigned fungi associated with pine recruitment.
3. Early seedling establishment was positively associated with multiple abiotic factors, while seedling survival was positively associated with the absence of a known pathogenic fungus and other biotic factors. Null model tests identified known mycorrhizal partners and a large number of unassigned operational taxonomic units (OTUs) associated with seedling survival, including mycorrhizal, saprotrophic and pathogenic species.
4. Synthesis: We conclude that high throughput metabarcoding paired with null model tests, is a valuable approach for identifying hidden plant-fungal associations within large and complex DNA metabarcoding datasets. Such an approach can be an important tool in illuminating the black box of plant-microbe interactions, and thus understanding ecosystem dynamics.

1. 植物与真菌的相互作用对植物群落组装至关重要，但量化此类关联仍颇具挑战。针对真菌群落的高通量测序技术，可实现高分辨率的植物-真菌关联鉴定，但通常无法获取真菌的分类学与功能注释信息。
2. 本研究将瑞士五针松（Pinus cembra）的种子移植于海拔梯度（1850~2250米，以海平面为基准）的生境中，筛选出对幼苗建成与存活至关重要的环境因子及已知真菌共生伙伴；随后通过空模型检验，鉴定出与松树幼苗定植相关的未分类学注释真菌。
3. 幼苗早期建成与多种非生物因子呈正相关，而幼苗存活则与已知致病真菌的缺失及其他生物因子呈正相关。空模型检验结果显示，已知菌根共生伙伴及大量未分类学注释的操作分类单元（operational taxonomic units，OTU）与幼苗存活相关，其中涵盖菌根类、腐生类及致病类真菌。
4. 综合分析表明：将高通量宏条形码测序与空模型检验相结合，是在大型复杂DNA宏条形码测序数据集中识别隐藏植物-真菌关联的有效方法。该手段可作为阐明植物-微生物相互作用黑箱的重要工具，进而助力理解生态系统动态变化。