Net CO2 Assimilation Rate and Nitrogen Content of Grape Leaves Subsequent to Fruit Harvest

Abstract

Abstract The relationship between net CO2 assimilation rate (A) and nitrogen (N) content during leaf senescence was determined on field grown Vitis vinifera L. ‘Thompson Seedless’ leaves. Measurements commenced subsequent to fruit harvest and were made at weekly intervals until leaf fall. Maximum A was greater than 2.0 nmoles CO2 cm-2s-1 when leaf N content was greater than 3.0%. There was a linear relationship between A and percent N content regardless of whether A was expressed on an area or dry weight basis. However, the correlation between A on a dry weight basis and percent leaf N was greater than that between A on an area basis and percent leaf N. The percent N content and net CO2 assimilation rate decreased as weight per unit leaf area (W) increased. There was no effect on leaf N content on stomatal conductance (gs) when N content was greater than 2%. The results suggest that leaf N content could be used an as indicator of a grapevine's leaf photosynthetic capacity subsequent to fruit harvest.