Photosynthetic Response of Carrots to Varying Irradiances, CO2 Concentrations, Moisture, and Nutrition

Abstract

<jats:p>Genotypes and environmental parameters interactively act on plants and modify their yield responses through modifying photosynthetic processes. In order to optimize yield, it is critical to understand the photosynthetic behavior of the crop as altered by genotypes and environment. Leaf gas exchange parameters of carrot (<jats:italic>Daucus carota</jats:italic> L.) cultivars Cascade, Carson, Oranza, and Red Core Chantenay (RCC) were examined in response to various irradiances, fertility levels, moisture regimes, and to elevated CO<jats:sub>2</jats:sub> concentrations. Leaf net photosynthetic rate (P<jats:sub>N</jats:sub>), stomatal conductance (g<jats:sub>s</jats:sub>), and transpiration rate (E) were measured. Cultivars responded similarly to increasing <jats:italic>PAR</jats:italic> and CO<jats:sub>2</jats:sub> concentrations and did not differ in photosynthetic parameters. Increasing <jats:italic>PAR</jats:italic> from 100 to 1000 μmol·m<jats:sup>-2</jats:sup>·s<jats:sup>-1</jats:sup> increased P<jats:sub>N</jats:sub>, which did not reach saturation. The g<jats:sub>s</jats:sub> and E increased to a peak between 600 and 800 &amp;#956;mol·m<jats:sup>-2</jats:sup>·s<jats:sup>-1</jats:sup>, then rapidly declined, resulting in a sharp increase in water use efficiency (WUE). Increasing CO<jats:sub>2</jats:sub> concentrations from 50 to 1050 μmol·mol<jats:sup>-1</jats:sup> increased P<jats:sub>N</jats:sub> until saturation at 650 μmol·mol<jats:sup>-1</jats:sup>. The g<jats:sub>s</jats:sub> and E increased to a peak at 350 μmol·mol<jats:sup>-1</jats:sup> and then declined. WUE increased linearly with increasing CO<jats:sub>2</jats:sub>. Carrots exposed to drought over a period of 5 days decreased P<jats:sub>N</jats:sub> and E. The P<jats:sub>N</jats:sub> decrease was cultivar specific. Nutrient concentrations of 0 to 400 ppm gave a similar pattern of decrease for P<jats:sub>N</jats:sub>, E, and g<jats:sub>s</jats:sub>. Treatment of 50 ppm had the highest P<jats:sub>N</jats:sub>, E, and g<jats:sub>s</jats:sub>. The WUE generally increased with increasing nutrient concentration.</jats:p>