Synergizing high-sugar traits and interspecific diversity: temporal dynamics and trade-offs in temperate grasslands

Temperate grasslands are essential for sustainable ruminant production, yet their seasonal stability and nutritional balance are increasingly threatened by climate shifting. While high-sugar ryegrass (HSG) cultivars and grass-legume mixtures offer solutions to these constraints, their integrated performance across productivity, quality, and stability dimensions requires holistic evaluation.

This study conducted a field experiment in Aberystwyth, UK, employing a two-factor design with five grass components (three HSG cultivars, a tri-mixture, and a standard control) and two sowing modes (pure grass vs. white clover mixtures). Across nine harvests, we assessed temporal dynamics in dry matter (DM) yield, community composition, and nutritive value. Additionally, the Coupling Coordination Degree, food equivalent unit (FEU), and food equivalent unit productivity (PFEU) were comprehensively evaluated as independent indices to quantify trade-offs and synergies.

The pure-sown HSG cultivar AberMagic (AM) maximized early-season DM yield (9144.48 kg·ha^-1) but experienced significant mid-season declines. Conversely, grass-clover mixtures mitigated this "summer slump" via temporal niche differentiation, significantly improving yield stability and biological weed suppression (grass weeds< 0.5%). Nutritional analysis revealed a physiological trade-off: pure HSG stands delivered superior energy density through elevated water-soluble carbohydrates (WSC), whereas mixtures provided a more balanced nutritional profile, significantly increasing late-season crude protein (CP) to 22.20%-28.05% and reducing neutral detergent fiber (NDF).

Management models must align with specific agronomic goals. Pure AM is the premier choice for intensive systems prioritizing maximum total output. For long-term grazing requiring a stable feed supply, the AberAvon (AA) and white clover (WC) mixture is optimal due to its exceptional late-season recovery and excellent synergistic performance across indicators. Furthermore, the consistent underperformance of standard varieties underscores the absolute necessity of utilizing improved traits. Synergizing the ecological resilience of multi-species mixtures with the improved traits establishes an optimal framework for sustainable and highly coordinated forage systems.