Element allocation in fungal mycelia
The ability to reduce or increase N and P concentrations (in parallel) within the fungal mycelium may be related to spatial patterns (e.g. retranslocation/recycling) or a general decline throughout the mycelium. In fungal mycelia grown on SEA we indeed observed different C:N ratios in inner versus outer regions of mycelia (Fig. 5a) due to twofold increases in relative N concentrations in outer parts (Fig. S8). Since high N concentrations were only present in the outer, more recently produced and likely more active mycelium portion, the relative amount of N decreased during fungal growth causing also temporal shifts in C:N ratios (Fig. 5b, Fig. S8). We tested whether this simple element allocation pattern also explained non-homeostatic shifts in C:N ratios due to limiting N supply (Fig. 1), namely a simple spatial reduction of the outer N-rich zone (Fig. 6). Again, all fungal isolates had lower C:N (and also C:P) ratios in outer mycelial parts, however, this differential allocation was not affected by N supply rates (Fig. 5c, Fig. S9). Shifts in fungal C:N ratios occurred equally in inner and outer mycelial parts (Fig. S9).