Positive plant diversity effects on soil detritivore feeding activity and stability increase with ecosystem age

Increasing species diversity frequently enhances ecosystem functioning - a pattern strengthened with ecosystem age. It has been suggested that strengthened responses over time may be due to community assembly processes and cumulative effects over the history of interactions between and among plant and soil communities. However, most soil studies are conducted with destructive one-time samplings, and little is known about how phenological patterns of soil activity change with biodiversity and ecosystem age. Here, we investigate phenology metrics related to soil detritivore feeding activity (i.e., duration, total magnitude, variability), measured via the bait-lamina method, in a long-term grassland biodiversity experiment that included an experimental removal of plant and soil history, resulting in older and younger assembled plant and soil communities. Detritivore feeding activity peaked in spring and/or early summer, with another short increase in fall. Increased plant species richness enhanced the total magnitude and variability (i.e., the coefficient of variation) of detritivore feeding activity. Plant and soil history enhanced the buffering effects of plant richness on variability, causing older plant and soil communities to have the strongest relationships between plant richness and stability. However, older plant and soil communities showed the shortest duration of detritivore feeding activity, and species richness was not important in changing activity duration. These findings underscore the importance of considering ecosystem age as a critical component that modifies plant diversity effects on ecosystem functioning, with important implications for promoting ecosystem stability and resilience under environmental change.