Understanding the underlying mechanisms behind the positive biodiversity-productivity relationship is one of the most pressing questions in ecology. Historically, the implicit mechanism of the majority of biodiversity ecosystem function studies was resource partitioning in response to interspecific competition. While studies demonstrating indirect evidence for resource partitioning are numerous, explicit evidence for resource partitioning is weak. Furthermore, while a plethora of studies implicitly and explicitly quantify competition among plants aboveground, competition in roots, which represent up to 70% of community biomass in grassland ecosystems, remains understudied. If interspecific competition for belowground resources is a dominant structuring force, species should alter their root allocation across belowground strata to avoid other species’ resource use (spatial resource partitioning). Yet, evidence for spatial resource partitioning in roots is inconclusive.
We provide an explicit belowground test of spatial resource partitioning for 13 grassland species across five soil depths in a long-term biodiversity-ecosystem function field experiment.
Results/Conclusions
In contrast to common predictions for competitive interactions, we found that as species richness increased, species aggregated in the top soil layer rather than segregating across depth. These results imply that alternative mechanisms, such as feedback from biota or abiotic facilitation are likely more important drivers of the positive plant diversity-productivity relationship than spatial resource partitioning belowground.