Huck M G, Ishihara K, Peterson C M, Ushijima T
United States Department of Agriculture, Agricultural Research Service, Auburn University, Auburn, Alabama 36849.
Plant Physiol. 1983 Oct;73(2):422-7. doi: 10.1104/pp.73.2.422.
Soybean (Glycine max [L.] Merr. cv Braxton) plants were grown in sandy soil with only natural rainfall (N) or with supplemental irrigation (I). Water-stressed plants grew more extensive root systems, whereas irrigated plants developed larger shoots and smaller root systems. Maximum stomatal apertures were observed at the beginning of each photoperiod. Partial stomatal closure occurred each afternoon, but stomata of I plants remained open longer than those of N plants. Significant reductions in net carbon fixation rate generally accompanied decreases in stomatal aperture, which coincided with periods of high temperature, low relative humidity, maximum solar radiation, and water stress. Leaf water potential decreased from morning to afternoon, with a greater decrease observed for N plants. Midafternoon stomatal closure did not occur in N plants with very large root systems following a heavy rain which saturated the soil profile. With smaller root systems and greater evaporative demand from larger shoots, the I plants continued to show midafternoon stress following the heavy rain. The large root systems of the N plants absorbed sufficient water to meet shoot evaporative demand for several days following the rain. Root soil system resistance apparently contributed to the afternoon water stress in the I plants.
大豆（Glycine max [L.] Merr. cv Braxton）植株种植于仅靠自然降雨（N）的沙质土壤中或补充灌溉（I）的沙质土壤中。水分胁迫的植株根系生长更为广泛，而灌溉植株地上部分生长较大但根系较小。在每个光周期开始时观察到最大气孔孔径。每天下午气孔会部分关闭，但灌溉植株的气孔比自然降雨植株的气孔开放时间更长。净碳固定率的显著降低通常伴随着气孔孔径的减小，这与高温、低相对湿度、最大太阳辐射和水分胁迫时期相吻合。叶片水势从早晨到下午下降，自然降雨植株的下降幅度更大。一场大雨使土壤剖面饱和后，根系非常庞大的自然降雨植株在下午未出现气孔关闭现象。由于根系较小且地上部分蒸发需求较大，灌溉植株在大雨后下午仍持续出现胁迫现象。自然降雨植株庞大的根系吸收了足够的水分，以满足雨后数天地上部分的蒸发需求。根系土壤系统阻力显然导致了灌溉植株下午的水分胁迫。
