Studies on the Hydrophysiological Rhythms of Citrus Trees

II. Seasonal Effects of Carbon Dioxide on the Cyclic Fluctuations of Leaf Thickness

Abstract

With a differential transformer, changes in leaf thickness of one-year-old potted Natsudaidai seedlings were observed throughout the year. The cyclic fluctuations of leaf thickness were at first slight but became noticeable in the middle of May. During the summer season, the amplitude was increased more. In early December, however, the rhythms became irregular with depressed fluctuations and finally disappeared when the season advanced. It was also observed that the amplitude of cyclic fluctuations quickly responded to changes in the carbon dioxide concentration in the air, i.e., the amplitude increased with increasing carbon dioxide concentration up to about 1, 000ppm. On the contrary, when the carbon dioxide concentration was lowered to that of the normal air, the original magnitude was recovered. Such responses of the leaf to changes in carbon dioxide concentration were not observed in the period from winter to spring. From the results obtained, it was postulated that root activity might considerably affect stomatal movement.