ACKNOWLEDGEMENT
The authors acknowledge the help provided by the ‘NMR for Life’ infrastructure supported by the Wallenberg Foundations, the SITES (Swedish Infrastructure for Ecosystem Science) and ICOS research infrastructures (for maintaining the Kulbäcksliden/Degerö Stormyr facility) funded by the Swedish research council (VR), the SciLifeLab infrastructure, the SLU Stable Isotope Laboratory (for C- and N-isotope and elemental analysis), Umeå Plant Science Center (for providing the growth chambers), assistance from Jan Karlsson in operating the growth chambers, assistance from Prof. Larry Flanagan in calculation ofc c, and financial support from the Knut and Alice Wallenberg Foundation (#2015.0047), VR and the Carl Tryggers Foundation.