The pitfalls of ectomycorrhizal microcosms: lessons learnt for future success

Mycorrhizal fungi are known to support their host plants by facilitating nutrient acquisition and enhancing resistance to biotic and abiotic stress. However, the possibility that they also convey structural information about the soil has not yet been tested. Here, we attempted to investigate whether ectomycorrhizal hyphae could guide root growth in response to physical obstacles by using Scots pine (<i>Pinus sylvestris</i>) and <i>Suillus granulatus</i> in a microcosm experiment fitted with U-shaped silicone mazes. Despite initial success in achieving ectomycorrhizal colonisation (88% of the inoculated seedlings), the fungi failed to produce the expected hyphal networks. Extensive and unexpected root growth rendered the system unsuitable for testing our hypothesis. Furthermore, structural issues with the microcosms compromised substrate integrity, possibly inhibiting fungal development. While our results were inconclusive, this report highlights challenges associated with replicating classical ectomycorrhizal experiments, underscoring the need for methodological refinement. We provide detailed recommendations and methodological clarifications that may aid future research. Although our initial hypothesis could not be tested, we argue that traditional microcosm experiments retain potential for advancing our understanding of mycorrhizal ecology, provided they are critically revisited and technically improved. Negative results, when well contextualised, are valuable contributions toward more robust and reproducible experimental frameworks.

菌根真菌（Mycorrhizal fungi）已知可通过促进养分获取及增强宿主植物对生物与非生物胁迫的抗性来提供支持。然而，它们是否也能传递土壤结构信息这一可能性尚未得到验证。在此，我们通过在装有U型硅胶迷宫的微宇宙实验（microcosm experiment）中使用欧洲赤松（<em>Pinus sylvestris</em>）和颗粒牛肝菌（<em>Suillus granulatus</em>），尝试探究外生菌根菌丝（ectomycorrhizal hyphae）能否引导根系生长以应对物理障碍。尽管外生菌根定殖初期取得成功（接种幼苗的88%），但真菌未能形成预期的菌丝网络。根系意外且过度的生长导致该系统不适用于验证我们的假设。此外，微宇宙装置的结构问题破坏了基质完整性，可能抑制了真菌的发育。尽管我们的结果尚无定论，但本报告强调了复制经典外生菌根实验所面临的挑战，凸显了方法学改进的必要性。我们提供了详细的建议和方法学说明，以期为未来研究提供帮助。尽管我们的初始假设未能得到验证，但我们认为，若能对传统微宇宙实验进行批判性重新审视和技术改进，其仍有望推动我们对菌根生态学的理解。若能充分结合背景，阴性结果可为构建更稳健、可重复的实验框架提供宝贵贡献。