The Effect of Age on the Rate of Apparent Photosynthesis in Leaves of Tall Fescue (Festuca arundinaceaSchreb.)

Abstract

N apparatus is described in which the rate of apparent photosynthesis of single attached or detached grass leaves was determined by measuring with an infra-red gas analyser the uptake of carbon dioxide from a stream of air passed over the leaves. In one experiment the apparatus was used to determine the apparent photosynthesis at one time of the three youngest leaves removed from a tiller of tall fescue plants grown in the field. Results showed that each older leaf had a lower rate of apparent photosynthesis than its successor. To determine the real effect of age of the leaf without any possible interaction with position of the leaf or an after-effect of environment, measurements of apparent photosynthesis were made in two further experiments on leaves attached to the main stem on plants grown in controlled environments. Results were obtained from samples of the fifth leaf of increasing age from full expansion. These showed a progressive decline in apparent photosynthesis with increasing age: in one experiment this was preceded by a small initial rise after complete leaf expansion. There were no marked changes in the weight of the leaf as it aged and, in consequence, the form of the results were similar when expressed on either a leaf area or dry weight basis.