Effects of nitrogen deficiency on leaf photosynthesis, carbohydrate status and biomass production in two olive cultivars ‘Meski’ and ‘Koroneiki’

The effects of nitrogen deficiency on CO2 assimilation, carbohydrate content and biomass were studied in two olive (Olea europaea L.) cultivars (‘Meski’ and ‘Koroneiki’). One-year-old plants were grown in pots and subjected to four nitrogen levels for 58 days.Nitrogen-deficient plants had significant lower leaf nitrogen and chlorophyll a contents. They also showed a significant reduction in their photosynthetic capacity. A tolerance difference between cultivars was observed: ‘Meski’ proved to be more efficient in maintaining CO2 assimilation rates than ‘Koroneiki’ under nitrogen deficiency, which was reflected by increased photosynthetic nitrogen use efficiency. Accumulation of carbohydrates, especially starch, mannitol, sucrose and glucose, was observed in nitrogen-deficient leaves. This indicates that both the high carbohydrate and the low nitrogen content inhibit photosynthesis in nitrogen-deprived olive plants. Total biomass was strongly reduced (mainly caused by a decrease in leaf dry weight) under nitrogen deficiency for both cultivars, but root:shoot ratio was hardly affected. Elongation of fine roots was enhanced in ‘Koroneiki’ under severe nitrogen-deprivation.