Elevated Carbon Dioxide Level Suppresses Nutritional Quality of Lettuce and Spinach

Abstract

Rising global CO 2 levels are a major factor that impacts not only the environment but also many plant functions including growth, productivity and nutritional quality. The study examined the impact of elevated [CO 2 ] on nutritional quality and growth characteristics of lettuce ( Lactuca sativa ) and spinach ( Spinacia oleracea ). Elevated [CO 2 ] decreased the concentration of many important nutrients including nitrogen (protein), potassium and phosphorus in the edible parts of both lettuce and spinach. The nitrogen concentration in lettuce shoots was reduced by more than 30% at elevated [CO 2 ] compared to the plants grown at ambient level of CO 2 . Similarly the concentration of a number of micronutrients including sulfur, zinc, copper and magnesium, was depressed in lettuce shoots. Although the total phenolic content and antioxidant capacity were higher in lettuce at elevated CO 2 , they were not affected in spinach. The photosynthetic activity was variable among the plant species while there was no increase in the carbon accumulation in these plants at elevated [CO 2 ]. However, there was significant reduction in the leaf stomatal conductance in both lettuce and spinach in response to higher [CO 2 ], which is likely affect both water loss from the leaves and their photosynthetic activity. The results indicate a broad adverse impact of rising [CO 2 ] on the nutritional quality of commonly consumed leafy vegetables namely, lettuce and spinach.