[Effects of NO3- stress on photosynthetic characteristics and nitrogen metabolism of strawber- ry seedlings].

In order to explore the effects of NO3- stress on photosynthetic characteristics and nitrogen metabolism, strawberry seedlings were grown in sand culture condition under different concentrations of NO3- (64, 112 and 160 mmol · L(-1)) with the control of 16 mmol NO3- · L(-1). The results indicated that at the 8th day after treatment, with the increased NO3- concentration, the strawberry leaf net photosynthetic rate (Pn), stomatal conductance (g(s)), PS II actual photochemical efficiency (ΦPS II), PS II maximum photochemical efficiency (Fv/Fm), and photochemical quenching coefficient (q(P)) significantly decreased, and decreased by 67.7%, 68.4%, 35.7%, 23.2% and 26.9%, respectively, when NO3- concentration reached 160 mmol · L(-1) compared with the control. The non-photochemical quenching coefficient (q(N)) increased by 4.4%, 10.9% and 75.8% respectively in the treatments of 64, 112 and 160 mmol NO3- · L(-1) compared with the control. The intercellular CO2 concentration (Ci) decreased under low NO3- concentration stress and then increased under high NO3- concentration stress, while the stomatal limitation (Ls) was vice versa. With the increased NO3- concentration, the nitrate nitrogen, ammonia nitrogen, total nitrogen and Kjeldahl nitrogen contents in the strawberry leaves and roots increased, but the protein nitrogen content decreased. The activities of nitrate reductase (NR) , glutamine sybthetase (GS), glutamate synthase (GOGAT) and glutamate dehydrogenase (GDH) increased at low NO3- concentration and then decreased at high NO3 concentration. Consequently, the net photosynthetic rate of strawberry seedling leaves decreased, the PS II electron transfer was blocked, the nitrogen accumulated with the increasing NO3- concentration, and the nitrogen metabolism enzyme activity decreased at high NO3- concentrations. When the NO3- concentration reached 64 mmol · L(-1) or higher in the nutrient solution, the growth of strawberry seedlings were inhibited significantly.