EFFECTS OF NITROGEN ON THE PHOTOSYNTHETIC APPARATUS OF CLEMATIS-VITALBA GROWN AT SEVERAL IRRADIANCES

Effects of nitrogen supply (N-supply) on the photosynthetic apparatus of Clematis vitalba L. grown at several irradiances were determined by measuring soluble protein content, rubisco activity, photosynthetic p igment content and composition, and the photochemical efficiency of ph otosystem II (FvFm). Compared to low irradiance (3 and 10% full sunlig ht), leaves grown at higher irradiance (up to full sunlight) had up to 5-6 times the soluble protein content and rubisco activity, and up to 2-4 times the total carotenoid content, on both a leaf area and a chl orophyll basis. On a leaf area basis, decreased N-supply reduced solub le protein concentration, rubisco activity and total carotenoid concen tration to a greater extent at high compared to low irradiance. On a c hlorophyll basis, in contrast, soluble protein and rubisco activity de creased by over 40% with increased N-supply (1.0-0.1 mol m(-3)) at hig h irradiance but N-supply did not influence the concentration of total carotenoids. Leaves grown at high compared to low irradiance had a gr eater concentration of xanthophyll cycle pigments (V+A+Z), beta-carote ne and lutein (but not neoxanthin) on a chlorophyll basis, and a sligh tly lower F-v/F-m. Nitrogen-supply did not influence the composition o f the photosynthetic pigment pool, F-v/F-m, or the extent of deepoxida tion of the V+A+Z pool. The results suggest that irradiance-acclimatio n of C. vitalba can occur regardless of N-supply. Under N limitation a t high irradiance, a balance between light capture and photosynthetic capacity is important rather than an increase in xanthophyll cycle-dep endent energy dissipation. The importance of lutein as a light-harvest ing pigment is questioned. A rapid method for the reversed phase-HPLC separation of carotenoids is described.