Spatial resource partitioning between species via differences in rooting depth is one of the main explanations for the positive biodiversity-productivity relationship. However, evidence for the importance of this mechanism is limited. This may be due to the community scale at which these interactions are often investigated. Community measures represent net outcomes of species interactions and may obscure the mechanisms underlying belowground interactions.

Here, we assess the performance of ~1700 individual plants and their heterospecific neighbours over three growing seasons in experimental grassland plots containing one, four or 16 different plant species and tested whether their performance in mixtures compared to monocultures was related to their own rooting depth vs. the rooting depth of their heterospecific neighbours.

Overall, individuals of deep-rooting species performed better in mixtures and this effect significantly increased when surrounded by more shallow-rooting species. This effect was not apparent for the shallow rooting species. Together, including both deep and shallow rooting species increased mixture performance.

Our results show that taking the perspective of the individual rather than the community can elucidate the interactions between species that contribute to positive biodiversity effects, emphasizing the need for studies at different scales to disentangle the myriad interactions that take place in diverse communities.

These data were collected following the methods found in Bakker et al. 2021 Oikos. All data processing needed to produce the analyses and figures in this manuscript are included with the code necessary to produce these figures and analyses. 

We have included a ReadMe file and notes throughout the code. Any additional questions can be directed to the corresponding author of the paper (Liesje Mommer) or Kathryn Barry.