This research examines how different genetic variations within a single fungal species affect its ability to form beneficial partnerships with poplar tree roots. Scientists studied 40 genetically distinct fungal strains derived from the same parent and found that they varied greatly in their success at colonizing tree roots, ranging from complete failure to excellent colonization. By analyzing the genes and gene expression of these strains, the team identified specific genetic regions that influence symbiosis formation and discovered that genetic diversity within this fungal species plays an important role in how effectively forest ecosystems function.