Abstract
Legume-based forage plant mixtures are known to increase biomass production over the mixture species grown as pure stands (overyielding), which has partly been attributed to enhanced nitrogen availability by legumes. However, the relative importance of underlying processes of these positive diversity effects and their drivers are not fully understood. Here we assessed if outcome and causes of diversity effects depend on the legume-species genetic identity. Over five years, we cultivated different white clover (Trifolium repens) populations, a grass and forb species in pure stands and clover-based mixtures and recorded biomass yield. Complementarity and selection effects of mixtures and relative yields of mixture species were calculated based on both unfertilized and nitrogen-fertilized non-leguminous pure stands. Results showed that the clover population altered the overall strength of diversity effects as well as the direction and magnitude of their temporal trends, at least for the grass component of mixtures. Differences in diversity effects between clover populations diminished when fertilized instead of unfertilized non-leguminous pure stands were considered. Hence, a part of these differences likely results from dissimilar effects of clover populations on nitrogen availability. The findings reveal the possibility to improve overyielding of legume-based forage plant mixtures by decisions on legume-species genetic identity.
Highlights
Legume-based forage plant mixtures are known to increase biomass production over the mixture species grown as pure stands, which has partly been attributed to enhanced nitrogen availability by legumes
Considering unfertilized non-leguminous reference stands, CE and selection effect (SE) depended on white clover population, whereas NE did not (Table 1a)
We show that the choice of the white clover population substantially affects outcome and causes of diversity effects and their temporal trends, though not consistently across all scales
Summary
Legume-based forage plant mixtures are known to increase biomass production over the mixture species grown as pure stands (overyielding), which has partly been attributed to enhanced nitrogen availability by legumes. Complementarity and selection effects of mixtures and relative yields of mixture species were calculated based on both unfertilized and nitrogen-fertilized non-leguminous pure stands. Which species and how strongly these profit from being cultivated in mixtures (overyield in mixture) is crucial to uncover the underlying processes of mixture overyielding[21] This especially applies to mixtures including legumes, as legumes are often a main driving force of mixture o veryielding[13,22] but are prone to competitive replacement by their non-leguminous mixture p artners[12,23]. Integrated assessments of overall (e.g. NE) and individual diversity effects (e.g. RYC) are still not common for experimental communities close to agriculturally used g rassland[25], especially not so for those including non-leguminous forbs[26]
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