Root traits and plasticity differences explain complementarity between co-existing species in phosphorus-limited grassland

Background and Aims: The complementarity and selection effects are important in the diversity-productivity relationship. The diversity of functional traits among species has an important effect on complementarity. However, it remains to be explored which root functional traits play a central role in explaining biomass production and whether the variation in trait plasticity caused by environmental changes affects the interspecific complementarity effects. Methods: We characterized three leaf and 10 root traits related to P acquisition in four temperate grassland species with various resource foraging strategies in a study featuring monocultures and two-species mixtures in a greenhouse with two P-limited (20 mg P kg⁻¹ soil as C₆H₆Na₁₂O₂₄P₆ or KH₂PO₄) and one P-adequate (200 mg P kg⁻¹ soil as KH₂PO₄) environments. Results: Majority of mixed communities produced significant net biodiversity and complementarity effects that varied among species combinations and P supplies. In the two P-limited treatments, the functional dispersion of single root traits (root volume, root diameter, root:shoot ratio, or exudation of acid phosphatase or organic acid anions) and plasticity difference in single traits (root length, root volume, root surface area, or exudation of organic acid anions) among the species explained the variation in the complementarity effect. However, the difference in the multi-trait space based on all 13 traits and their plasticity had no correlation with the complementarity effect regardless of P supply. Conclusion: Our results suggested that differences in key root traits and plasticity among species played an important role in driving complementarity effects between plant species.