CONCLUSIONS

The stimulating effects of plant diversity on plant biomass (Loreau & Hector 2001; Hooper et al., 2005; Cardinale et al., 2013; Liang et al., 2016), root productivity (Ma & Chen 2016; Ravenek et al., 2014; Oram et al., 2017), and soil fauna activity (Birkhofer et al., 2011; Spehn et al., 2000) have been shown before. However, our high temporal resolution data show that plant diversity effects on plant and soil processes change throughout the year. Root production is initiated during winter, right after the end of the aboveground growing season. With this, the positive plant diversity effects on aboveground processes may result from earlier plant diversity effects on the root system operating over winter. Unraveling the patterns of aboveground-belowground phenological synchrony offers a significant promise to advance underexplored areas of plant and soil ecology by adding an essential layer to understanding aboveground-belowground interactions (Ochoa-Hueso et al. 2021). In the context of biodiversity and ecosystem functioning, aboveground-belowground phenology may broadly advance the interpretation of species coexistence. It can help propose new mechanisms on whether and how biodiversity enhances ecosystem functioning. Overall, this work shows fundamental differences in the phenological patterns of leaf and root production and the activity of soil organisms, stressing the role of plant diversity in modulating the phenology of plant processes and soil fauna activity.