Effects of CO2 enrichment on yield, carbohydrate accumulation and changes in the activity of antioxidative enzymes in bell pepper (Capsicum annuum L.)

Abstract

SummaryCO2 enrichment is an important means of maximizing the yield and quality of vegetables grown in greenhouses. In bell pepper grown in CO2-enriched greenhouses, the plant leaves frequently exhibit leaf rolling (LR) and chlorosis. In the present study we investigated the relationship between the occurrence of these symptoms and changes in several metabolic activities in leaves of three bell pepper (Capsicum annuum L.) cultivars that differ in their susceptibility to LR under CO2 enrichment. LR and leaf chlorosis in CO2 enriched pepper plants affected ‘Cuby’ more than ‘Fiesta’ and ’Turkal’. This was compatible with the observation that the increment in fruit yield due to CO2 enrichment in `Cuby’ was less than that of the other two cultivars. The severity of LR and leaf chlorotic symptoms was enhanced by complete defruiting of the plants, especially under CO2 enrichment. Both the enrichment and defruiting treatments enhanced daily leaf starch accumulation. In leaves of pepper plants ‘Cuby’, CO2 enrichment enhanced the ascorbic acid content that had been attenuated by defruiting. Leaf catalase activity was increased four fold in CO2-enriched plants but this effect was completely eliminated in defruited plants. The superoxide dismutase (SOD) activity underwent similar but much smaller changes. The results suggest that the symptoms in the leaves of pepper plants may be caused by excessive accumulation of carbohydrates, especially starch, in response to long-term CO2 enrichment. Under these circumstances formation and accumulation of free radicals may occur. The relationship between these metabolic responses and the occurrence of LR and leaf chlorosis is discussed.