Abstract: This experiment aimed to explore the relationship between plant population density and photosynthetic performance and yield of winter rye in a cold region. The variety used was ‘Dongnong winter rye 001’, and the experiment comprised 5 replicates sowing densities (D₁, 225×10⁴ plants·ha^-1; D₂, 275×10⁴ plants·ha^-1; D₃, 325×10⁴ plants·ha^-1; D₄, 375×10⁴ plants·ha^-1; D₅, 425×10⁴ plants·ha^-1), arranged in a completely random design. Leaf chlorophyll content measured using a SPAD meter (CCM-200+) reached the maximum at the heading stage. With increased crop density, the SPAD value decreased, and the density-induced decrease was more pronounced after anthesis. The maximum values of net photosynthetic rate, stomatal conductance, transpiration rate and intercellular carbon dioxide concentration of rye leaves occurred at the flowering stage. With increasing crop density, many photosynthetic parameters, including the maximum photochemical efficiency (F_v/F_m), the actual photochemical efficiency (Φ_PSⅡ) and the photochemical quenching coefficient (q_P) showed progressive reduction; however, the non-photochemical quenching coefficient (q_N) increased. The yield of fresh and hay winter rye (Secale) were highest at D₃, after which the biomass yield decreased with increasing density. It is concluded that establishing the correct population density (D₂) to obtain higher photosynthetic capacity before flowering is the basis for obtaining high yield of winter rye in cold regions.

Key words: winter rye, plant density, photosynthetic characters, chlorophyll fluorescence, yield