| Abstract: The effect of potassium defi ciency on lettuce was studied in order to fi nd out the reason of its normal appearance and slow growth. With 'Batavian' lettuce as the material, four gradients of potassium supply were set through nutrient solution management method, which were the normal amount (CK) and the 1/2, 1/4, 1/8 amount of normal potassium supply, respectively. The changes of potassium content, soluble sugar content and photosynthesis of lettuce leaves under potassium defi ciency treatment were analyzed. The results showed that the net photosynthetic rate, stomatal conductance, intercellular carbon dioxide concentration and transpiration rate of lettuce in 1/2 and 1/4 treatment were not signifi cantly different from those of CK, while those of 1/8 treatment were signifi cantly lower than those of CK. Under 1/2, 1/4, 1/8 treatments, the potassium content in the inner and outer leaves of lettuce gradually decreased, and the soluble sugar content gradually increased. With the decrease of potassium content in leaves, both the ratio of potassium content in outer and inner leaves and the ratio of soluble sugar content in outer and inner leaves all increased, which indicated that when lettuce suffered from potassium defi ciency, more functional substances were allocated to the outer leaves to maintain its normal function, while the inner leaves grew slowly due to less distribution. |