[Influence of enhanced UV-B radiation on chlorophyll fluorescence characteristics of soybean]

To investigate the influence of enhanced UV-B radiation on chlorophyll fluorescence characteristics of soybean, pulse amplitude modulation fluorometer was employed to measure the fluorescence parameters and rapid light curves during different growth stages under the condition of simulating 20% enhancement of UV-B. Results showed that enhanced UV-B radiation reduced the chlorophyll contents by 5.03%, 7.70% and 10.38% in seedling, branching-flowering and pod-setting periods, respectively. In branching-flowering period, the value of Fv/Fm decreased by 6.13%. In seedling and branching-flowering periods, effective quantum yield(Y) diminished significantly during PAR >366 micromol x (m2 x s)(-1), the maximal potential relative electron transport rate (Pm) diminished by 28.92% and 15.49%, respectively. But Y and Pm had no significant difference in 3-leave and pod setting periods. Semi-light saturation points (l(k)) were diminished by 21.18% and 23.17% in 3-leave and seedling periods. Initial slope (a) was decreased by 21.05% in branching-flowering period. Enhanced UV-B radiation also significantly reduced non-photochemical quenching (NPQ) during PAR >366 micromol x (m2 x s)(-1) in seedling period and photochemical quenching (qP) during PAR >366 micromol x (m2 x s)(-1) in branching-flowering period. The results of this study suggested that enhanced UV-B radiation inhibited electron transport activity of PS II, injured light-harvesting systems and dissipative protection mechanisms, damaged photosynthesis system, thus diminished photosynthetic efficiency of soybean.