Plant attributes interact with fungal pathogens and nitrogen addition to drive soil enzymatic activities and their temporal variation

O_LINitrogen enrichment can alter soil communities and their functioning directly, via changes in nutrient availability and stoichiometry, or indirectly, by changing plant communities or higher trophic levels. In addition, soil biota and their associated functions may show strong temporal changes in their response to environmental changes, yet most current studies have only focused on one of these potential drivers or have measured soil functioning only once during the peak growing season. Therefore, we know little about the relative importance of the different mechanisms by which nitrogen enrichment affects soil communities, functioning and temporal stability. C_LIO_LIIn a large grassland experiment manipulating nitrogen enrichment, plant species richness, functional composition and foliar pathogen presence, we measured activities of two enzymes, {beta}-glucosidase and acid phosphatase, as indicators of soil functioning. We did so across different seasons and years to assess their temporal dynamics and how consistently they responded to multiple drivers. C_LIO_LINitrogen addition was the most important driver of {beta}-glucosidase activity, and it increased {beta}-glucosidase activity over time. However, interactions between plant attributes and fungicide application were the main drivers of acid phosphatase activity. The temporal stability of soil enzyme activity was differently affected by two facets of plant diversity (species richness [+] and functional diversity [-]), with nitrogen and fungicide addition dampening these effects. C_LIO_LISynthesis: Fungicide effects, and their interactions with plant diversity, show the importance of foliar pathogens not only for above-but also for belowground processes, and highlight the possibility that these plant enemies are major modulators in the relationships between plant diversity and ecosystem functioning. We also show the need to consider temporal dynamics in belowground processes to better understand the responses of ecosystem functioning to environmental changes such as nutrient enrichment. C_LI