Specific leaf area, leaf nitrogen content, and photosynthetic acclimation of Trifolium repens L. seedlings grown at different irradiances and nitrogen concentrations

Clover seedlings were grown at different nitrogen concentrations (5, 10, 15, 20, 25 mM NO₃ ⁻, i.e. N₅ to N₂₅) and two irradiances, I (200 and 400 μmol m⁻² s⁻¹ of photon flux density, i.e. I ₂₀₀ and I ₄₀₀). Net photosynthetic rate (P N), photosynthetic nitrogen use efficiency (PNUE), leaf chlorophyll (Chl) content, maximum photochemical efficiency (Fv/Fm), and actual photochemical efficiency of photosystem 2 (PS2) (ΦPS₂) increased from N₅ to N₁₅ and decreased with N₁₅ to N₂₅. P N, PNUE, and ΦPS₂ were higher at I ₄₀₀ than at I ₂₀₀, but Fv/Fm and leaf Chl contents at I ₄₀₀ were lower than at I ₂₀₀. The effects of the N and I on specific leaf area (SLA) and N contents per unit dry mass (Nm) were similar, the SLA and Nm increased from N₅ to N₂₅ and they were higher at I ₂₀₀ than at I ₄₀₀. The nitrogen contents per unit area (Na) increased from N₅ to N₂₀, but decreased from N₂₀ to N₂₅. The Na was higher at I ₂₀₀ than at I ₄₀₀ when Trifolium repens grew at N₅ and N₁₀, but it was higher at I ₄₀₀ than at I ₂₀₀ at N₁₅ to N₂₅.