[This nonGeographicDataset is embargoed until December 1, 2025]. This dataset encompasses 1) Detailed measurements of root architecture parameters - numerical values for Total length (cm), Area (cm²), Surface area (cm²), Average diameter (mm); Root volume (cm³), Number of tips, forks, and crossings; and 2) The physiological responses of poplar trees under varying light conditions - measurements of Transpiration rate (mmol m⁻² s⁻¹), Net CO₂ assimilation rate (µmol m⁻² s⁻¹), Intercellular CO₂ concentration (µmol mol⁻¹), Intercellular CO₂ partial pressure (Pa), and Stomatal conductance to water vapour (mol m⁻² s⁻¹). Data were generated in a glasshouse experiment under elevated CO₂ (740 µmol mol⁻¹). The Root Architecture data was collected when the trees were six months old. Net Photosynthesis Light Curves were recorded at four time points, starting when the poplar trees were two months old and continuing until they were six months old. The root architecture data were obtained through WinRhizo scanning and software (Regent Instruments Inc., Quebec City, QC, Canada). The physiological measurements were recorded using LI-6800P Portable Photosynthesis System (LI-COR Biosciences, Lincoln, NE, USA). To construct the light curves, measurements were taken starting from a maximum light intensity of 1500 PPFD (µmol m⁻² s⁻¹) and subsequently decreased to 800, 200 and 50 µmol m⁻² s⁻¹ until no light was applied. In this experiment, micro-propagated poplar clones were cultivated under four different conditions: without fungi (fungal-free plants), with ectomycorrhizal fungi (ectomycorrhizal plants), with saprotrophic fungi (saprotrophic fungal plants), and with both ectomycorrhizal and saprotrophic fungi (fungal plants). The purpose of the experiment was to evaluate plant performance under the influence of different fungal guilds and their interactions. Full details about this nonGeographicDataset can be found at https://doi.org/10.5285/82721bfc-d707-4255-bc5b-4d5882f9881b