以盆栽玉米（掖单４号）幼苗为材料，在土壤缓慢干旱但无昼夜温差条件下，研究了叶片Ψｗ、Ψｓ、Ψｐ和叶片伸长速度的昼夜变化。结果表明干旱条件下，白天叶片伸长速度大于夜间叶片伸长速度；白天叶基部Ψｐ值高于夜间Ψｐ值；白天叶基部的高Ψｐ_值是Ψｓ值增加（即渗透调节作用）所致。Ψｐ值较高是白天叶片伸长速度较高的重要原因。 Diurnal changes of Ψw, Ψs, Ψp and leaf elongation of leaves were studied using potted corn (Yedan No.4) seedlings under the conditions of slow and dry soil without temperature difference between day and night. The results showed that under dry conditions, the leaf elongations at daytime were higher than those at night. The basal Ψp values ​​at daytime were higher than those at night Ψp values. The high Ψp value at the basal daytime was due to the increase of Ψs (ie osmoregulation). The high value of Ψp is the important reason for the higher leaf elongation during the daytime.