Nitrogen fertilisation and light effects on growth and photosynthesis of lodgepole pine seedlings

Seedlings of Pinus contorta were grown for 16 wk without ectomycorrhizas in the greenhouse at three levels of irradiance (100, 210 and 470 μEm^-2s^-1) and three levels of ammonium nitrate (3, 62 and 248 mg litre^-1 of N). Measurements at 5, 10 and 16 wk of age indicated that plants receiving the highest levels of irradiance and nitrogen had significantly larger biomass, a higher total foliar N and P content and net photosynthesis per unit leaf area than those at lower levels of each factor. Although the root/shoot ratio also increased from low to high irradiance at each harvest, nitrogen application resulted in an increased ratio from 3 to 62 mg litre^-1 N, but decreased ratio at 248 mg litre^-1 N.