Isotopic data from: Coupled shifts in ectomycorrhizal communities and plant uptake of organic nitrogen along a soil gradient: an isotopic perspective

Plants associating with mutualistic ectomycorrhizal (ECM) fungi may directly obtain nitrogen (N) bound in soil organic matter (N-SOM). However, the contribution of N-SOM to plant growth under field conditions remains poorly constrained. We tested the hypothesis that turnover in ECM communities along soil inorganic N gradients mediates a functional transition from plant reliance on N-SOM in low inorganic N soils, to primarily inorganic N uptake in inorganic N rich condition soils. We quantified the d15N of Q. rubra foliage and roots, organic and inorganic soil N pools, and used molecular sequencing to characterize ECM communities, morpho-traits associated with N-foraging, and a community aggregated sporocarp d15N. In support of our hypothesis, we document the progressive enrichment of root and foliar d15N with increasing soil inorganic N supply; green leaves ranged from -5.95‰ to 0.16‰ as the supply of inorganic N increased. ECM communities inhabiting low inorganic N soils were dominated...