Abstract: Effects of different nitrogen deficiency degree on leaf photosynthesis characteristics and physiological indices of watermelon were studied by using watermelon Heitong K8 as the experimental material， which would provide basis for measuring and diagnosing the degree of nitrogen deficiency and nitrogen fertilization. The results indicated that contents of chlorophyll and soluble protein in leaves of watermelon decreased significantly along with the decrease of nitrogen application amount， and as well as the net photosynthetic rate （Pn） and stomatal conductance in leaves and total biomass， while the ratios of root to shoot were increased. These results showed that the growth and photosynthetic and physiological characteristics of watermelon were obviously inhibited under nitrogen deficiency. Results of chlorophyll fluorescence research showed that Fv/Fm， Sm， ETo/CSo and RC/CSo of watermelon leaves under the nitrogendeficiency treatments were obviously lower than the control leaves， in which Sm was the most sensitive index. However， there was no significant difference among ABS/CSo， TRo/CSo and DIo/CSo under nitrogendeficiency treatments. In addition， correlation analysis indicated that the correlations of Sm and Pn， Fv/Fm and total biomass reached extremely significant level. These results suggested that the chlorophyll fluorescence measurements could detect the changes of photosynthesis of nitrogendeficiency watermelon leaves， and could be used to diagnose the degree of nitrogen deficiency.

Key words:  watermelon, photosynthetic characteristics, chlorophyll fluorescence