Maintaining a higher level of ecosystem multifunctionality requires soil biodiversity in a temperate old growth forest

Background/Question/Methods: Ample empirical evidence has shown that biodiversity affects the simultaneous performance of multiple ecosystem functions (that is, ecosystem multifunctionality). However, diversity-manipulation experiments necessarily simplify the complexity of natural ecosystems and will normally control for other important drivers of ecosystem functioning, such as the environment. We currently know little, however, about the determinants and mechanisms of forest multifunctionality, which is of practical importance for ensuring the sustainable provision of multiple functions.

Results/Conclusions: We measured eight ecosystem functions (aboveground biomass stock, coarse woody productivity, litterfall production, seed production, herb species richness, soil organic carbon density, litter and soil saturation moisture capacity), and their the full spectrum of abiotic and biotic drivers, including soil nutrients, species diversity, trait composition, stand structure attribute, and soil biodiversity in 120 plots in an old-growth temperate forest of Changbai region in northeast China. Structural equation modelling (SEM) was applied to assess the multiple abiotic and biotic pathways of ecosystem multifunctionality under the predictions from multiple theories into a single model.

We found the following: a) we provided strong support for abiotic factor (i.e. soil nutrients), the mass ratio (i.e. trait composition), the niche differentiation effect based on stand structure complexity and phylogenetic diversity for averaged-based multifunctionality, whereas no support for soil diversity effect; b) Trait composition with conservative species rather than acquisitive species were positively related to both averaged-based and threshold-based ecosystem multifunctionality in this old-growth temperate forest; c) though the relative contributions of abiotic and biotic predictors on ecosystem multifunctionality varied across different thresholds, the soil diversity was the key determinants of higher level of ecosystem multifunctionality (75% threshold-based multifunctionality).Our results indicate that the shape and strength of the relationship between tree diversity and multiple functions depends critically on ecosystem multifunctionality measurement approaches. Our findings provide empirical evidence that any loss in species, structural or microbial diversity will likely reduce the provision of forest ecosystems.