Changes in the foliar fungal community between oak leaf flushes along a latitudinal gradient in Europe

Aim: To advance our understanding of how foliar fungal communities are structured and assembled, we assessed to what extent leaf flush and latitude can explain the within- and among-tree variation in the foliar fungal community in a foundation tree species, the pedunculate oak Quercus robur.

Location: A latitudinal gradient spanning c. 20 degrees in latitude in Europe.

Major taxa studied: The foliar fungal community on Quercus robur.

Methods: We examined the main and interactive effects of leaf flush and latitude on the foliar fungal community by sampling 20 populations of the pedunculate oak Quercus robur across the tree’s range, spanning c. 20 degrees in latitude.

Results: Species composition, but not species richness, differed between leaf flushes. Across the latitudinal gradient, species richness was highest in the central part of the oak’s distributional range, and foliar fungal community composition shifted along the latitudinal gradient. Among fungal guilds, the relative abundance of plant pathogens and mycoparasites was lower on the first leaf flush, and the relative abundance of plant pathogens and saprotrophs decreased with latitude.

Conclusions: Changes in community composition between leaf flushes and along the latitudinal gradient were mostly a result of species turnover. Overall, our findings demonstrate that leaf flush and latitude explain 5-22% of the small- and large-scale spatial variation in the foliar fungal community on a foundation tree within the temperate region, with major consequences for plant health, species interactions and ecosystem dynamics.

研究目的：为深化对叶际真菌群落（foliar fungal community）构建与结构调控机制的认知，本研究以建群树种夏栎（Quercus robur）为研究对象，量化评估展叶期（leaf flush）与纬度梯度分别可在多大程度上解释该树种叶际真菌群落在单株树内及树间的变异。
研究区域：横跨欧洲约20个纬度跨度的纬度梯度（latitudinal gradient）样带。
研究类群：夏栎（Quercus robur）的叶际真菌群落。
研究方法：我们在夏栎的自然分布范围内，沿约20个纬度梯度采集了20个种群的样本，以此分析展叶期与纬度对叶际真菌群落的主效应及交互效应。
研究结果：不同展叶期的叶际真菌群落物种组成存在显著差异，但物种丰富度无显著区别。在整个纬度梯度上，叶际真菌物种丰富度在夏栎分布区的中部达到峰值，且群落组成随纬度梯度发生系统性演替。在真菌功能群（fungal guilds）层面，首次展叶期的植物病原菌（plant pathogens）与重寄生真菌（mycoparasites）相对丰度更低；同时植物病原菌与腐生真菌（saprotrophs）的相对丰度随纬度升高而降低。
研究结论：不同展叶期及纬度梯度下的叶际真菌群落组成变化主要由物种更替（species turnover）驱动。综上，本研究结果表明，展叶期与纬度可解释温带区域内建群树种叶际真菌群落在小尺度与大尺度空间上5%~22%的空间变异（spatial variation），该发现对植物健康、物种互作及生态系统动态均具有重要意义。