Relation of stoichiometric shifts with fungal growth and activity
In a defined glucose medium characterized by N or P limitations alone,
varying fungal C:N:P values were good linear predictors of fungal growth
and activity (Fig. S2, Table S4 and S6). In parallel to shifts in
element concentrations, biomass production, fungal density and enzymatic
activity were positively affected by higher N supply, as well as biomass
and density by increasing P supply (Fig. S2). Thus, models examining the
explanatory power of fungal C:N and C:P ratios distinguished them as
good predictors of fungal growth, activity and the ratio of phosphatase
and leucine-aminopeptidase production (Table S4 and S5).
By contrast, in complex media with more diverse C sources, observed
strong shifts in C:N and C:P values did not allow to predict N or P
limitations. Along varying N supply with cellulose as a C source, fungal
traits did not respond positively to increasing N availability, showing
no indication of N limitation despite high fungal C:N values (Fig. S3).
Likewise, in soil extract agar the addition of N and P alone did not
affect biomass production or fungal density, nor did it show a
significant interaction with the addition of cellulose or glucose (Fig.
2b, c). By contrast, cellulose and glucose additions shifted fungal
biomass from 7.8 mg (± 2.7) to 19.9 mg (± 2.1) and 64.4 mg (± 10.6),
respectively. Only enzymatic activity responded positively to N
additions, while glucose strongly suppressed fungal enzymatic activity
also in the presence of additional N (Fig. 2d). Consequently,
stoichiometric ratios did not correlate with fungal growth or activity
in cellulose and SEA media.