Arctic plants are affected by many stressors. Root-associated fungi are thought to influence plant performance in stressful environmental conditions. However, the relationships are not well-known; do the number of fungal partners, their ecological functions and community composition mediate the impact of environmental conditions and/or influence host plant performance? To address these questions, we used a common arctic plant as a model system: Bistorta vivipara. Whole plants (including root system, n = 214) were collected from nine locations in Spitsbergen. Morphometric features were measured as a proxy for plant performance and combined with metabarcoding datasets of their root-associated fungi (amplicon sequence variants, ASVs), edaphic and meteorological variables. Seven biological hypotheses regarding fungal influence on plant measures were tested using structural equation modelling. The best-fitting model revealed that local temperature affected plants both directly (negatively aboveground and positively below-ground) and indirectly - mediated by fungal richness and the ratio of symbio- and saprotrophic ASVs. The influence of temperature on host plants is therefore complex and should be examined further. Fungal community composition did not impact plant measurements and plant reproductive investment was not influenced by any fungal parameters. The lack of impact of fungal community composition on plant performance suggests that the functional importance of fungi is more essential for the plant than their identity.

北极植物受到许多胁迫因素的影响。人们认为，与根相关的真菌会在压力环境条件下影响植物的生长性能。但是，这种关系并不为人所知。真菌伴侣的数量，其生态功能和群落组成是否介导环境条件的影响和/或影响寄主植物的性能？为了解决这些问题，我们使用了常见的北极植物作为模型系统：Bistorta vivipara。从斯匹次卑尔根的9个地点收集了整株植物（包括根系，n = 214）。测量形态特征作为植物性能的代名词，并与它们的根相关真菌（amplicon序列变体，ASV），营养和气象变量的元条形码数据集结合起来。使用结构方程模型测试了关于真菌对植物措施影响的七个生物学假设。最佳拟合模型表明，局部温度直接（负向地上和正向地下）地和间接地影响植物，这是由真菌丰富度以及共生和腐生ASV的比例介导的。因此温度对寄主植物的影响是复杂的，应进一步研究。真菌群落组成不影响植物的测量，植物繁殖投资不受任何真菌参数的影响。真菌群落组成对植物生长性能的影响不足表明，真菌的功能重要性对植物而言比其身份更重要。