从叶水势、气孔开度和叶可溶性醣量日变化动态方面研究了大田小麦“午睡”的原因。认为:叶水势下降及其所引起的气孔开度减小是形成午睡的重要原因。叶水势降至-14巴,光合作用迅速下降,气孔开度急速变小;气孔开度减到2μm 以下则影响光合速率。中午叶可溶性醣过量积累则抑制光合作用,此亦“午睡”原因之一。 The reasons for the “napping” of field wheat were studied from the aspects of leaf water potential, stomatal opening and leaf digestibility. It is concluded that the decrease of leaf water potential and the decrease of stomatal opening are the important reasons for the formation of nap. Leaf water potential dropped to -14 bar, photosynthesis decreased rapidly, stomatal opening rapidly decreased; stomatal opening reduced to 2μm below the photosynthetic rate. The excessive accumulation of soluble sugar at midday leaves inhibits photosynthesis, which is also one of the reasons for “nap”.