The effect of the mixture is globally synergistic across exposure scenarios
Synergistic effects dominated the process of decomposition across exposure scenarios, with the number of nonadditive effects largely surpassing the probability of retrieving significant differences by chance. Of the 206 differences between data pairs of expected and observed values (seven litter processing variables across the three exposure scenarios), 92% differed from zero, of which 55% were positive and 37% were negative. The mixture promoted higher-than-expected colonisation by decomposers (60% of data pairs) and detritivores (57% of data pairs), while mass loss was globally additive (41% of data pairs positive and 59% negative). The effect of the mixture on decomposers resulted mostly from the increased sporulation rates, but, to a lower extent, also from the increased number of species. Concerns on the consequences of biodiversity loss for ecosystem structure and function have driven much of the research on the effect of mixing litter, but interestingly only a few studies include measures of how riparian biodiversity loss may affect diversity of the detritus-based food webs (but see Abelho, 2009; two studies reviewed by Gartner & Cardon, 2004; Chapman et al., 2013). The synergistic effect of the mixture on fungal richness may indicate that the simplification of riparian diversity will be followed by microbial diversity loss, as suggested by Chapman et al. (2013).
The global synergistic effect across exposure scenarios clearly shows that mixing litter stimulated colonisation by decomposers and detritivores, but not mass loss, once again highlighting that mass loss or breakdown rates do not fully capture the effect of mixing litter on the process of decomposition.