Chlorophyll fl uorescence responses to a factorial combination of nitrogen (N) and phosphorus (P) supply were measured in fi ve clones of Pinus radiata cultivated in a greenhouse over twenty-four months. Chlorophyll fl uorescence measurements were taken at months six (5 clones, 182 plants), nine (2 clones, 68 plants) and eighteen (2 clones, 48 plants). Plant growth in stem diameter, height, leaf area, fascicle mass, length and diameter were found to signifi cantly increase with N and, to a lesser extent, P additions; and these values were greatest when both N and P were combined. Plant growth and fascicle size also varied signifi cantly across clones and were generally consistent with the genotypic growth responses that were observed in the fi eld. Dark (Fv/Fm) and light-adapted (ΦPSII) photochemical effi ciency of PSII were found to signifi cantly increase with N and, to a lesser extent, P addition; and the combined effects of N and P exceeded those of the individual contributions. Stern-Volmer nonphotochemical quenching, which relates to the proportion of energy dissipated as heat, did not signifi cantly increase as plants became more N or P defi cient. Chlorophyll fl uorescence variables did not differ between clones. We found positive linear relationships between photosynthetic rates at 360 μmolּmol-1 CO2 concentration and 1500 μmol photons m-2ּs-1 of irradiance (Asat), Fv/Fm and ΦPSII and both foliar nitrogen (Na) and phosphorus (Pa) concentration on a leaf area basis when a ratio of Na/Pa equal to 23 molּ mol-1 was used to partition N from P defi ciencies. These relationships were independent of genotype. Chlorophyll fl uorescence and gas exchange estimates of electron transport were well correlated under ambient photorespiratory conditions, suggesting that chlorophyll fl uorescence variables are a good surrogate for gas exchange measurements in our experimental conditions.