Effects of Nitrogen Exponential Fertilization on Photosynthetic Characteristics of Three Catalpa bungei Clones

In order to understand the photosynthetic physiological characteristics of different Catalpa bungei clones and to determine the optimum nitrogen rate,three Catalpa bungei clones(1-4,7080,and 015-1) were used to study the dynamic changes of photosynthetic characteristics under four levels of exponential fertilization.The results showed that:(1)The net photosynthetic rate,transpiration rate and the stomatal conductance of the three C.bungei clones by nitrogen treatment were higher than that of the CK in three months.The net photosynthetic rate of clones 1-4,7080,and 015-1 were 36.63%-89.66%,9.35%-70.87%,and 14.92%-66.12% higher than that of the CK.The water use efficiencies of clones 1-4,7080,and 015-1 in July and August were 30.14%-57.38%,19.05%-53.85%,and 12.69%-47.54% higher compared with that of the CK.(2)The photosynthetic parameters of clones 1-4,7080,and 015-1 in June and July increased with the increasing of nitrogen application rate,and showed the trend of up-down in August.(3)Various exponential fertilization could promote the photosynthetic capacity of C.bungei clones,and the effects of 10 g urea·plant-1 were the best.In August,the net photosynthetic rates and water use efficiencies of clones 1-4,7080,and 015-1 were 13.76,17.36,and 12.82 μmol·m-2·s-1,3.84,4.60,and 3.60 μmol·mmol-1.The photosynthetic capacity and water use efficiency of clone 7080 were better than that of clone 1-4 and 015-1.