Fig. 1. Hypothesized contribution of different nitrogen (N) forms to tree growth (red and orange lines; y-axis) and tree responses to historic increases in CO₂ (iCO₂).

These responses occur along a gradient of varying supply rates of inorganic N (net N mineralization rates: x-axis). Dark blue arrows show the relativized fertilization response (arrow width) to iCO₂. ECM fungal community composition, morpho-traits, and community aggregated decay traits (CADT) estimated using metagenomic approaches, are  hypothesized to vary with soil inorganic N availability. Note hypothesized turnover in the dominance of ECM taxa with extra-radical rhizomorphic hyphae and long-and medium-distance exploration morphologies. White speckles on roots depict hypothesized relative abundance of ECM root-tips. Illustration by Callie R. Chappell, with permission from Reinhard Agerer.