Effect sizes were calculated as the log response ratio between observed and expected values for each response variable and 95% bootstrap confidence intervals (CI) are shown. Data at each harvest time of the decomposition experiment were used to calculate the effect size of each variable. We created intervals of 10% increments in mass loss up to 70% of mass loss, but did not distinguish further the final interval from 70% to 100%, because of only few observations within this range of mass loss. The slightly different positions of symbols within each interval is to better differentiate among curves of mass loss, N release, and P release and has no other meaning. The solid horizontal black line indicates no effects (mean effect size = 0, observed values = expected values). Mean effect size >0 indicates synergistic effects (observed values > expected values), while mean effect size <0 indicates antagonistic effects (observed values < expected values). The non-additive effects (synergistic or antagonistic) are significant at α = 0.05 if the CI of the effect size does not overlap with the zero line, while the effects are additive when there is overlap. Values in parentheses above the symbols denote the number of observations and asterisks indicate a significant mixture effect (i.e. a significant deviation from 0).