Interactions between plants and arbuscular mycorrhizal fungi (AMF) are pivotal in linking belowground soil nutrients with plant-derived carbon in terrestrial ecosystems. However, little is known about the effect of variation in soil nutrients (i.e., nitrogen enrichment) on the structure and phylogenetic characteristics of the mutualistic network. With a 7-year nitrogen addition experiment in an alpine meadow, we built networks for 20 plant species that all occur along the nitrogen addition gradient and their AMF by sequencing 314 root samples. We investigated the responses of association degree (i.e., the number of links of plant or AMF species), network connectance, nestedness, modularity and specialization to different concentrations of nitrogen addition. Phylogenetic signal was calculated to evaluate if the phylogenetically closely related plant species or AMF taxa share similar symbiosis partners. We found that nitrogen addition significantly reduced the plant and AMF association degree, with the generalist (with high association degree) and abundant AMF taxa in nature significantly decreasing association degree and relative abundance (sequencing reads). Therefore, the network connectance and nestedness decreased, but modularity increased with nitrogen addition. Phylogenetic signal of plants (i.e., phylogenetically related plants had similar AMF partners) was always stronger than that of AMF, but the signal vanished with nitrogen addition. The shifted soil properties after nitrogen addition, especially pH, played an important role in regulating the network structures. Our results discover a non-random plant-AMF network shaped by both phylogeny and soil environments in an alpine meadow, and suggest that global nitrogen addition may result in a non-random loss or switch of plant-fungal associations, changes in network structures and phylogenetic relationships, which may have ramification to nutrient exchange and symbiotic performance.

植物和丛枝菌根真菌 (AMF) 之间的相互作用对于将地下土壤养分与陆地生态系统中植物衍生的碳联系起来至关重要。然而，关于土壤养分变化（即氮富集）对互惠网络的结构和系统发育特征的影响知之甚少。通过在高寒草甸进行为期 7 年的氮添加实验，我们通过对 314 个根样本进行测序，为 20 种植物建立了网络，这些植物都沿着氮添加梯度及其 AMF 发生。我们研究了关联度（即植物或AMF物种的链接数）、网络连接、嵌套性、模块化和专业化对不同浓度的氮添加的响应。计算系统发育信号以评估系统发育密切相关的植物物种或 AMF 分类群是否具有相似的共生伙伴。我们发现氮添加显着降低了植物和AMF的关联度，自然界中的通才（具有高关联度）和丰富的AMF分类群显着降低了关联度和相对丰度（测序读数）。因此，网络连接性和嵌套性降低，但模块性随着氮的添加而增加。植物的系统发育信号（即系统发育相关的植物具有相似的AMF伙伴）总是强于AMF，但随着氮的添加信号消失。施氮后土壤性质的变化，尤其是 pH 值，在调节网络结构中发挥了重要作用。