Experimental design
We incubated isotopically enriched litter in soil ingrowth cores and traced the fate of litter C and N into SOM over one growing season. Our experimental design included 3 levels of root/hyphal ingrowth (root and fungal ingrowth, root exclusion and fungal ingrowth, and root and fungal exclusion) and 3 fertilization treatments (no fertilization, high-level inorganic fertilization, or organic fertilization). We randomly selected 5 plots from each fertilization treatment from those which had successful rhizome establishment during initial plot development. Within each plot, we replicated each ingrowth core treatment twice, resulting 6 cores per plot (SI Fig. 2b ). This resulted in a total of 90 experimental ingrowth cores (3 cores x 3 fertilization treatments x 5 plots x 2 plants/plot).