Influence of nitrogen on leaf chlorophyll content and photosynthesis of ‘Golden Delicious’ apple

Abstract

The aim of the present study was to estimate the influence of different rates of soil-applied nitrogen on leaf N and chlorophyll content and photosynthesis in ‘Golden Delicious’ apple trees. Three different treatments were included: the trees were either fertilized with 80 kg N ha⁻¹ (N-80), 250 kg N ha⁻¹ (N-250) or left unfertilized (CON). Fertilization increased leaf nitrogen content, with a more prominent effect in high N application level treatment. In all treatments, a slight seasonal decrease in leaf nitrogen content was observed. N-250 treatment resulted in higher chlorophyll content; a similar effect was found late in the season for N-80 treatment. Measurements of A-C _i curves, performed on spur leaves, revealed a higher CO₂ saturated photosynthetic rate in N-250 trees compared with low application level fertilized or unfertilized trees. No effect of N fertilization on carboxylation efficiency was found, as revealed by comparisons of the initial slopes of A-C _i curves. The lack of positive effect is rather surprising, since the leaf N content was efficiently increased with application of fertilizer. Obviously, the existing pool of leaf nitrogen in non-fertilized trees does not limit Rubisco activity and efficiency.

Keywords:

• A-Ci curve
• nitrogen
• chlorophyll
• SPAD

Acknowledgements

This work is a part of the Horticulture No P4-0013-0481 program granted by the Slovenian Ministry of Higher Education, Science and Technology.