Increases in the flux of carbon belowground stimulate nitrogen uptake and sustain the long-term enhancement of forest productivity under elevated CO2

John E. Drake, Anne Gallet-Budynek, Kirsten S. Hofmockel, Emily S. Bernhardt, Sharon A. Billings, Robert B. Jackson, Kurt S. Johnsen, John Lichter, Heather R. McCarthy, M. Luke McCormack, David J. P. Moore, Ram Oren, Sari Palmroth, Richard P. Phillips, Jeffrey S. Pippen, Seth G. Pritchard, Kathleen K. Treseder, William H. Schlesinger, Evan H. DeLucia, Adrien C. Finzi