Data analysis
We used multiple linear regression to assess the effects of site, ECM dominance and the interaction between the two on root-derived C or root production separately. To focus on differences between AM and ECM-dominated plots, we also conducted two-way ANOVA tests using just the six end-member plots (AM or ECM-dominated). Site, plot type and the interaction between the two were included as fixed factors and root production or root-derived C were dependent variables. In the case of root-derived C, no significant interaction between site and plot type was observed and was subsequently removed as an independent variable. In the case of root-derived MAOM-C, only plot type was significant and a Student’s t-test was used to compared group differences. Student’s t-tests were also used to assess global plot type differences. Tukey’s post-hoc tests were used to evaluate pair-wise differences in each case. All analyses were carried out using R version 3.6.1 (R Core Team, 2019).