Effects of leaf movement on leaf temperature, transpiration
and radiation interception in soybean under water stress conditions
Akihiro Isoda and Peiwu Wang*
(Chiba University, *Shihezi Agricultural and Environmental Institute
for Arid Area in Central Asia, Shihezi, Xinjiang, China)
Abstract
Varietal differences in leaf movement were examined in terms
of radiation interception, leaf temperature and transpiration
under water stressed conditions. Five cultivars (Qindou 7232,
Gaofei 16, Dongnong 87-138, 8285-8 and 8874) were grown in a concrete
frame field in Xinjiang, China. Irrigation treatments (irrigation
and no irrigation) were made from flowering to the pod filling
stage. A leaflet in the uppermost layer of the canopy was restrained
horizontally. Leaf temperatures, transpiration rate (stem sap
flow rate of the main stem per unit leaf area) and intercepted
radiation of each leaflet were measured. There were greater varietal
differences in leaf movement, leaf temperature and transpiration
rate. Leaf temperature seemed to be adjusted by leaf movement
and transpiration. The extent to which is adjusted by leaf movement
and transpiration differed among the cultivars; leaf temperature
was influenced mainly by leaf movement for Gaofei 16 and Dongnong
87-138, mainly by transpiration for Qindou 7232 and 8874, and
by both for 8285-8. Intercepted radiation in the upper two layers
of the canopy (20 cm from the uppermost) was greater in the irrigated
plot, although the mean values of total leaflets of the irrigated
plot were not different as compared to the non-irrigated plot.
Although paraheliotropic leaf movement decreased radiation interception,
it offers some possibilities for the improvement in radiation
penetration within a dense canopy. Cumulated amount of transpiration
during a day was compared between the restrained-leaf and the
non-leaf-restrained plants in 8874. Paraheliotropic leaf movement
reduced water loss by 23 % in the irrigated and 71% in the non-irrigated
plots.