UWA School of Agriculture and Environment, and Institute of Agriculture, The University of Western Australia, 35 Stirling Hwy, Crawley (Perth), WA, 6009, Australia.
School of Veterinary & Life Sciences, Murdoch University, 90 South Street, Murdoch, WA, 6150, Australia.
Mycorrhiza. 2017 Oct;27(7):619-638. doi: 10.1007/s00572-017-0782-z. Epub 2017 Jun 7.
Fine root endophytes (FRE) are arbuscule-forming fungi presently considered as a single species-Glomus tenue in the Glomeromycota (Glomeromycotina)-but probably belong within the Mucoromycotina. Thus, FRE are the only known arbuscule-forming fungi not within the arbuscular mycorrhizal fungi (AMF; Glomeromycotina) as currently understood. Phylogenetic differences between FRE and AMF could reflect ecological differences. To synthesize current ecological knowledge, we reviewed the literature on FRE and identified 108 papers that noted the presence of FRE and, in some, the colonization levels for FRE or AMF (or both). We categorized these records by geographic region, host-plant family and environment (agriculture, moderate-natural, low-temperature, high-altitude and other) and determined their influence on the percentage of root length colonized by FRE in a meta-analysis. We found that FRE are globally distributed, with many observations from Poaceae, perhaps due to grasses being widely distributed. In agricultural environments, colonization by FRE often equalled or exceeded that of AMF, particularly in Australasia. In moderate-natural and high-altitude environments, average colonization by FRE (10%) was lower than that of AMF (35%), whereas in low-temperature environments, colonization was similar (~20%). Several studies suggested that FRE can enhance host-plant phosphorus uptake and growth, and may be more resilient than AMF to environmental stress in some host plants. Further research is required on the functioning of FRE in relation to the environment, host plant and co-occurring AMF and, in particular, to examine whether FRE are important for plant growth in stressful environments. Targeted molecular primers are urgently needed for further research on FRE.
细根内生真菌（FRE）是目前被认为属于单个物种——Glomus tenue 的丛枝菌根真菌（Glomeromycotina），但可能属于毛霉门。因此，FRE 是目前已知的唯一不属于丛枝菌根真菌（AMF；Glomeromycotina）的丛枝形成真菌。FRE 和 AMF 之间的系统发育差异可能反映了生态差异。为了综合当前的生态知识，我们回顾了有关 FRE 的文献，并确定了 108 篇记录了 FRE 存在的论文，其中一些还记录了 FRE 或 AMF（或两者）的定殖水平。我们根据地理位置、宿主植物科和环境（农业、中度自然、低温、高海拔和其他）对这些记录进行了分类，并在元分析中确定了它们对 FRE 定殖根长度百分比的影响。我们发现，FRE 在全球范围内分布广泛，许多观察结果来自禾本科，这可能是由于禾本科植物分布广泛。在农业环境中，FRE 的定殖通常与 AMF 相当或超过 AMF，特别是在澳大拉西亚。在中度自然和高海拔环境中，FRE 的平均定殖率（约 10%）低于 AMF（约 35%），而在低温环境中，定殖率相似（约 20%）。有几项研究表明，FRE 可以增强宿主植物对磷的吸收和生长，并且在某些宿主植物中，可能比 AMF 更能抵抗环境压力。需要进一步研究 FRE 与环境、宿主植物和共存的 AMF 的功能，特别是要研究 FRE 是否对在胁迫环境中生长的植物很重要。需要迫切研究 FRE 的靶向分子引物。
