Effects of the available nitrogen on the photosynthetic activity and xanthophyll cycle pool of maize in field

Investigations were performed on the interrelation between the photoprotective role of the xanthophyll cycle and levels of N-supply in maize plants (Zea mays L. cv. Maya). Plants were grown in non-fertilised and fertilised plots, while the latter were supplied with 30, 60, 90, 120 and 150 kg ha−1 NH4NO3 and grown under natural conditions in the field. The photosynthetic carbon assimilation of plants with higher N-supply, as compared to that of plants with lower N-supply, showed no significant differences, although a peak of the CO2 assimilation rate was observed at 60 and 90 kg N ha−1 treatment levels. Maize plants with lower N-supply had a lower leaf Chl-content than plants with higher N-supply, which was accompanied by a reduced rate of photochemical efficiency of photosystem II and a high thermal energy dissipation activity, measured as non-photochemical fluorescence quenching. Plants supplied with lower doses of N were detected to have a greater fraction of xanthophyll cycle pool in the form zeaxanthin and antheraxanthin. With reduction of the N-supply levels an increase in the ratio of xanthophyll cycle pigments as related to total Chl was observed. These results suggest that with the decrease of N-supply there is an increasing need to dissipate the excess light energy in the chloroplasts of maize leaves through xanthophyll cycle.