Effects of increased N O-3-N application on PSⅡ function in leaves of Morus alba seedlings under Na2CO3 stress

In this study, we analysed the effects of increased nitrate (N O-3-N) (from 7.5 mmolL-1 to 17.5 mmolL-1) on the growth and photosynthetic characteristics of mulberry seedlings, which were subjected to alkaline salt (50 mmolL-1 Na2CO3) stress using hydroponic methods. The results showed that plants displayed obvious symptoms of injury when subjected to 50 mmolL-1 Na2CO3 stress. Furthermore, compared with the control, the photochemical reaction centre activity of PSⅡ in stressed seedlings was significantly decreased, and electron transport was affected to different degrees on both the donor side and receptor side of PS Ⅱ. Under Na2CO3 stress, increasing N O-3-N promoted photosynthetic electron supply and transmission capacity, enhanced the function of the oxygen complex in the electron donor of PS Ⅱ, and increased the acceptor electron capacity of the receptor library. In addition, increasing N O-3-N also improved the stability of leaf thylakoid membrane structure, promoted the distribution of more light energy to the photochemical reaction centre, and decreased the proportion of energy in the form waste heat dissipation. In conclusion, increasing N O-3-N enhanced the function of PS Ⅱ under 50 mmolL-1Na2CO3 stress, which ensured the normal operation of photosynthesis.