Lettuce leaf characteristics.

Mean leaf number, dry mass (DM) of the fifth fully expanded leaf (g), and specific leaf area (SLA; cm2∙g–1) of the fifth fully expanded leaf of ‘Rouxai’ and ‘Rex’. Treatment subscripts indicate the photon flux density (μmol∙m−2∙s−1) of blue (B; 400–499 nm), green (G; 500–599 nm), red (R; 600–699 nm), and far-red (FR; 700–799 nm) light. Each value represents the mean of two replications with eight biological samples per treatment and replication. Means with different letters are significantly different based on Tukey’s honestly significant difference test (α = 0.05).