Global effect of the mixture across exposure scenarios
There were no significant differences between expected and observed values of mass loss (Fig. 2a) and the relative mixture effect was additive across exposure scenarios (Fig. 3a). Most data points of alder distributed below (Fig. 2b) while most data points of poplar distributed above the 1:1 line (Fig. 2c), resulting in a significant interaction between mixture effect and exposure scenario (Table 2). Despite a significant difference between mass loss of poplar in the mixture and as single species (F1,66=5.17, p <0.05; Table 2), the relative individual performance was additive for both species (Fig. 3d,f).
Sporulation rates and fungal richness were significantly higher (F1,19>6.75, p <0.05; Fig. 2g,j; Table 2), while fungal biomass was significantly lower (F1,34=5.26, p <0.05; Table 2, Fig. 2d) in the mixture than the average of the single species. Overall, the relative mixture effect on decomposers was synergistic (RME: 0.91 – 4.64) across exposure scenarios (Fig. 3a), due to increased sporulation rates (RME: 2.51 – 14.44) and richness (RME: 0.56 – 1.90) while the effect on biomass was additive (Fig. 3b). For alder, there were no significant differences between expected and observed values of any of the fungal variables (Fig. 2e,h,k). For poplar, sporulation rates and richness were significantly higher (F1,40>4.75, p<0.05; Table 2, Fig. 2i,l) while fungal biomass was significantly lower (F1,52=7.36, p<0.01; Table 2, Fig. 2f) in the mixture than as single species. When all three fungal variables were considered together, the relative individual performance on decomposers was synergistic for both species (Fig. 3d,f), weaker for alder (RIP: 0.09 – 2.81) and stronger for poplar (RIP: 1.17 – 18.23). However, the effect on each of the fungal variables differed between the two species. In the case of alder, there was a huge variation in the deviation between observed and expected values of fungal biomass, with a synergistic effect for sporulation rates only (Fig. 3e) while in the case of poplar there was a huge variation in the deviation between observed and expected values of sporulation rates with additive effects for all three fungal variables (Fig. 3g).
Most data points of shredder colonisation were distributed above the 1:1 line (Fig. 2m,n,o) resulting in a synergistic relative mixture effect (RME: 0.48 – 1.37) on detritivores across exposure scenarios (Fig. 3a), due to increased shredder biomass (RME: 0.66 – 2.98) and abundance (RME: 0.23 – 1.35) while the effect on richness was additive (Fig. 3c).
The relative mixture effect on the process of decomposition (Fig. 6) was globally synergistic across exposure scenarios (RME: 0.70 – 1.79due to the increased decomposer and detritivore colonisation.