Effects of different nitrogen forms on photosynthetic rate and the chlorophyll fluorescence induction kinetics of flue-cured tobacco.

摘要

The effects of N forms in the nutrient solutions on chlorophyll fluorescence and photosynthesis in tobacco (cv. K326) were studied. Net photosynthetic rate in tobacco plants grown with NH4-N as the only N source was lowest all the times, while that of plants grown only with NO3-N was greatest until the 22nd day. On the 24th day, the net photosynthetic rate was greatest when plants were grown with both NO3-N and NH4-N (1:1). Maximum photochemical efficiency of photosystem 2, variable fluorescence/maximum fluorescence (Fv/Fm), and actual quantum yield of PS2 under actinic irradiation in plants grown with only NH4-N were greatest at the early stage, then decreased and became smaller than those recorded for the other treatments. The photochemical quenching coefficient and non-photochemical quenching coefficient in the NH4-N plants were the greatest at all times. Thus, excessive NH4-N can decrease photochemical efficiency and efficiency of utilization of photon energy absorbed by pigments for photosynthesis. Therefore, excessive NH4-N is a hindrance to photosynthesis in flue-cured tobacco. On the other hand, tobacco cultured with an appropriate mixture of NO3-N with NH4-N can sufficiently utilize photon energy and increase the efficiency of energy transformation..