EFFECTS OF NITROGEN DEFICIENCY ON LEAF CHLOROPHYLL FLUORESCENCE PARAMETERS IN TWO OLIVE TREE CULTIVARS 'MESKI' AND 'KORONEIKI'

Effects of nitrogen (N) deficiency on photosynthetic carbon dioxide (CO2) assimilation, photosystem II (PSII) photochemistry and photoinhibition were investigated in young trees of two olive cultivars Meski' and Koroneiki' grown in a greenhouse under controlled conditions. The trees were subjected to four different levels of N supply. N deficient trees had a significantly smaller CO2 assimilatory capacity, but showed little changes in maximum quantum efficiency of PSII photochemistry. However, modifications in PSII photochemistry induced by N deficiency were observed. This was reflected in decreases in quantum yield of PSII electron transport (phi(PSII)) and efficiency of excitation energy capture by open PSII reaction centres (F-v'/F-m') and in an increase in non-photochemical quenching (NPQ). These results suggest that modifications in PSII photochemistry might be a mechanism to down-regulate photosynthetic electron transport so that production of adenosine triphosphate (ATP) and nicotinamide adenine dinucleotide phosphate (NADPH). would be in equilibrium with the decreased demand in the Calvin cycle in the N deficient trees. Therefore, both CO2 assimilation rate and total electron flow (J(t)) with its compound electron flows devoted to either carboxylation (J(c)) or oxygenation (J(o)) can be considered as useful tools to assess the N nutrition status of the trees. Clear relationships were found between A(max) and the nitrogen nutrition index (NNI) on the one hand, and between J(t) and NNI on the other hand. The results demonstrate that Meski' is more efficient than Koroneiki' when subjected to N deficiency.