H.E. Bown, E.G. Mason, P.W. Clinton, and M.S. Watt. 2009. Chlorophyll fluorescence response of Pinus radiata clones to nitrogen and phosphorus supply. Cien. Inv. Agr. 36(3):451-464. Chlorophyll fluorescence responses to a factorial combination of nitrogen (N) and phosphorus (P) supply were measured in five clones of Pinus radiata cultivated in a greenhouse over twenty-four months. Chlorophyll fluorescence 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 significantly 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 significantly across clones and were generally consistent with the genotypic growth responses that were observed in the field. Dark (F-v/F-m) and light-adapted (Phi(PSII)) photochemical efficiency of PSII were found to significantly 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 non-photochemical quenching, which relates to the proportion of energy dissipated as heat, did not significantly increase as plants became more N or P deficient. Chlorophyll fluorescence variables did not differ between clones. We found positive linear relationships between photosynthetic rates at 360 mu molmol(-1) CO2 concentration and 1500 mu mol photons m(-2)s(-1) Of irradiance (A(sat)), F-v/F-m and Phi(PSII) and both foliar nitrogen (N-H) and phosphorus (P-a) concentration on a leaf area basis when a ratio of N-u/P-a equal to 23 mol.mol(-1) was used to partition N from P deficiencies. These relationships were independent of genotype. Chlorophyll fluorescence and gas exchange estimates of electron transport were well correlated under ambient photorespiratory conditions, suggesting that chlorophyll fluorescence variables are a good surrogate for gas exchange measurements in our experimental conditions.