A conceptual framework and an empirical test of complementarity and facilitation with respect to phosphorus uptake by plant species mixtures

Plant species have different traits for mobilizing sparingly soluble phosphorus (P) resources, which could potentially lead to overyielding in P uptake by plant mixtures compared monocultures due higher as a result of resource partitioning and facilitation. However, there is circumstantial evidence at best these mechanisms. Overyielding (the outcome) easily confused with underlying mechanisms because unclear definitions. We aimed define conceptual framework separate outcome from test it facilitation complementarity respect acquisition three combinations grown on four soils. Our describes both outcomes (overyielding or no overyielding) depending the competitive ability mobilized P. Millet/chickpea were pots two calcareous soils mixed calcium-bound (CaP) phytate (PhyP). Cabbage/faba bean acid neutral P-coated iron (hydr)oxide (FeP) PhyP. Wheat/maize all Rhizosphere carboxylate concentration phosphatase activity (mechanisms) well biomass (outcome) determined rhizosphere mixtures. Facilitation occurred millet/chickpea one soil. found indications sources, neither millet/chickpea, nor cabbage/faba Cabbage faba soil differed concentration, but showed overyielding. Wheat maize, similar root exudates, observed being 22% than expected uptake) concluded that although differences physiological (root exudates) provide necessary conditions they do not necessarily increased mixtures, relative species.