Adaptive Responses of Soybean and Cotton to Diurnal Changes in Solar Radiation and Leaf Movement

Adaptive responses to diurnal changes in solar radiation and leaf movement restraint in soybean in comparison with cotton, which observes different heliotropism from that of soybean, were investigated in terms of leaf temperature (TL), Flow Rate of Stem Sap (FRSS), transpiration rate (E), stomatal conductance (gs) and stomatal aperture. Cotton showed higher FRSS and E while smaller TL than that of restrained (RLM) and Not-restrained Leaf Movement (NRLM) soybean. The RLM soybean showed higher FRSS, E at noon and TL than that of NRLM soybean. Larger FRSS and E of cotton could be attributed to its higher stomatal density, stomatal aperture, gs and the diaheliotropic leaf movement. In NRLM soybean, smaller FRSS and smaller E at noon as compared with RLM soybean might be due to the smaller abaxial stomatal aperture, gs and the paraheliotropic leaf movement. It was concluded that cotton responded to increase in diurnal solar radiation by increasing its transpiration to reduce TL. Increase in transpiration of cotton was due to increase in the size of stomatal aperture, gs and the diaheliotropic leaf movement. NRLM soybean responded to increase in solar radiation by observing paraheliotropism in order to reduce its TL while RLM soybean increased its transpiration in order to reduce TL. Increase in transpiration of RLM soybean was due to increase in abaxial stomatal aperture.