Fig. 2.

Loss of soil community functional complexity and nitrogen fertilization effects on the rates of five biogeochemical processes, compared with the response of average multifunctionality (Multifunc). The biogeochemical processes are net primary productivity (NPP); net ecosystem productivity (NEP); decomposition of a standard litter (S-litter); decomposition of litter returned within each replicate community (R-litter); and total community respiration (Respn). Each symbol represents the mean response to the complexity by fertilization treatments, and lines connect low- and high-complexity plots within control or nitrogen-fertilized subplots to facilitate the visualization of community effects. Values are standardized using a z-score transformation to permit comparison with the response of average multifunctionality and between processes with different units and absolute magnitudes. The statistical significance and coefficients of the complexity by fertilization treatments are given in Table 1 and the full process data in Fig. S1. Only standard litter decomposition responds in a qualitative manner (i.e., there is a positive complexity effect and no nitrogen or interaction effect) that is consistent with multifunctionality, but the absolute magnitude of the decomposition response to the community manipulation is much greater than for multifunctionality. The discontinuity between the individual process and multifunctionality responses raises questions about the practical and mechanistic interpretation of multifunctionality indices.