Effect of CO2 Concentration on Growth of Sugar-beet, Barley, Kale, and Maize

Abstract

Increasing the concentration of CO₂ in the air from the usual 300 ppm to 1, 000 ppm in growth rooms with temperatures of 20° C during the 16-h light period and 15° C during the 8-h dark period increased the total dry weight of sugar-beet, barley, and kale by about 5o per cent. A further increase in CO, concentration to 3, 300 ppm increased dry weight slightly more. These effects occurred with light intensities ranging from 3.7 to II.6 cal dm−² min−¹ of visible radiation supplied by a mixture of fluorescent and tungsten lamps, and were only slightly greater with the brighter light. Extra CO₂ also increased leaf area, though relatively less than dry weight, and the number of barley shoots but not of sugar-beet or kale leaves; it decreased leaf-area ratio, specific leaf area, and the ratio of tops to roots. Maize was taller with extra CO₂. Net assimilation rates in 1, 000 and 3, 300 ppm CO₂ were about 20 and 30 per cent respectively greater than in 300 ppm. Uptake of CO₂ in the light by complete tops and single leaves also increased with increase in CO₂ concentration. Photosynthesis of leaves of plants recently transferred to a new CO₂ concentration depended only on that concentration and not on the original one. Doubling the light intensity from 3.7 to 7.7 cal dm−² min−¹ affected dry weight, leaf area, net assimilation rate, etc., similarly to a tenfold increase in CO₂ concentration.