Acclimation to High CO 2 in Monoecious Cucumbers

Abstract

CO2 concentrations of 1000 compared to 350 microliters per liter in controlled environment chambers did not increase total fruit weight or number in a monoecious cucumber (Cucumis sativus L. cv Chipper) nor did it increase biomass, leaf area, or relative growth rates beyond the first 16 days after seeding. Average fruit weight was slightly, but not significantly greater in the 1000 microliters per liter CO2 treatment because fruit numbers were changed more than total weight. Plants grown at 1000 and 350 microliters per liter CO2 were similar in distribution of dry matter and leaf area between mainstem, axillary, and subaxillary branches. Early flower production was greater in 1000 microliters per liter plants. Subsequent flower numbers were either lower in enriched plants or similar in the two treatments, except for the harvest at fruiting when enriched plants produced many more male flowers than the 350 microliters per liter treatments. CO2 enrichment increases growth and yield in many species. Compared to nonenriched cotton, high C02-grown plants had twice the dry weight at 40 d (18). Enrichment to 700 compared to 350 L' CO2 raised dry matter production from 14 to 73% in six agronomic species (7). Seed yield increased 56 to 81% in soybean cultivars (8) and 17% in wheat (9) with enrichment. There are numerous reports also of cucumber yields respond-ing to CO2 enrichment in greenhouses. In the Netherlands, enrichment of gynoecious cucumber plants to 790 Ml L' CO2 increased fruit weight 41% and fruit number 36% compared to plants grown at 245 Ml L' (10). In Japan (1 1) fruit weight of gynoecious cucumbers increased 31-to 40% with enrichment to 1130M L' C02. In a preliminary study, we compared growth at 350 and 675