LEAF ORIENTATION AND SUNLIT LEAF-AREA DISTRIBUTION IN COTTON

The diurnal leaf orientation behaviour of row-planted cotton plants (G ossypium hirsutum L. cv, 'DES 119') and its relationship to sunlit lea f area distribution at three stages of development were studied in the field, Electromagnetic digitizing was used for plant geometrical stru cture measurement for three periods of 2h during the day. Cotton leave s showed a diaheliotropic response throughout the day. This heliotropi c behaviour varied according to growth stage. In addition to changes i n orientation, leaves also moved in space. The distance moved by a lea f between two observation times increased with stage of development, i n agreement with petiole and blade lengths. Sunlit leaf area distribut ion varied according to stage of development. Analysis of interception showed that probability of light interception was greater in the morn ing and in the afternoon than at noon. Without a diurnal change in can opy structure, cotton plants would intercept less direct radiation in the morning and in the afternoon. Leaf dispersion was regular during t he first and last stage of development, but it was clumped during the intermediate stage. Leaf dispersion was more regular in the morning an d the afternoon than at noon. Leaf dispersion, however, changed primar ily with sun direction and not with canopy structure. This would indic ate that small changes in leaf location do not significantly affect li ght interception. Finally, the ecological significance of diaheliotrop ism and the implications for modelling light interception in cotton pl ants are discussed. (C) 1997 Elsevier Science B.V.