Fine root endophytes (FRE) were traditionally considered a morphotype of arbuscular mycorrhizal fungi (AMF), but recent genetic studies demonstrate that FRE belong within the subphylum Mucoromycotina, rather than in the subphylum Glomeromycotina with the AMF. These findings prompt enquiry into the fundamental ecology of FRE and AMF. We sampled FRE and AMF in roots of Trifolium subterraneum from 58 sites across temperate southern Australia. We investigated the environmental drivers of composition, richness, and root colonization of FRE and AMF by using structural equation modelling and canonical correspondence analyses. Root colonization by FRE increased with increasing temperature and rainfall but decreased with increasing phosphorus (P). Root colonization by AMF increased with increasing soil organic carbon but decreased with increasing P. Richness of FRE decreased with increasing temperature and soil pH. Richness of AMF increased with increasing temperature and rainfall but decreased with increasing soil aluminium (Al) and pH. Aluminium, soil pH, and rainfall were, in decreasing order, the strongest drivers of community composition of FRE; they were also important drivers of community composition of AMF, along with temperature, in decreasing order: rainfall, Al, temperature, and soil pH. Thus, FRE and AMF showed the same responses to some (e.g. soil P, soil pH) and different responses to other (e.g. temperature) key environmental factors. Overall, our data are evidence for niche differentiation among these co-occurring mycorrhizal associates.

细根内生菌 (FRE) 传统上被认为是丛枝菌根真菌 (AMF) 的一种形态类型，但最近的遗传研究表明，细根内生菌 (FRE) 属于毛霉菌亚门，而不是具有 AMF 的球门真菌亚门。这些发现促使人们对 FRE 和 AMF 的基本生态进行探究。我们对三叶草根部的 FRE 和 AMF 进行了采样来自澳大利亚南部温带的 58 个地点。我们通过使用结构方程模型和规范对应分析研究了 FRE 和 AMF 的组成、丰富度和根系定植的环境驱动因素。FRE 的根系定植随着温度和降雨量的增加而增加，但随着磷 (P) 的增加而减少。AMF 的根系定植随着土壤有机碳的增加而增加，但随着 P 的增加而减少。FRE 的丰富度随着温度和土壤 pH 值的升高而降低。AMF 的丰富度随着温度和降雨量的增加而增加，但随着土壤铝 (Al) 和 pH 值的增加而减少。铝、土壤 pH 值和降雨量依次是 FRE 群落组成的最强驱动因素；它们也是 AMF 群落组成的重要驱动因素，以及温度、按降序排列：降雨量、铝、温度和土壤 pH 值。因此，FRE 和 AMF 对某些（例如土壤磷、土壤 pH 值）表现出相同的反应，而对其他（例如温度）关键环境因素表现出不同的反应。总体而言，我们的数据是这些共生菌根关联物之间生态位差异的证据。