Effects of NO3--N on growth and photosynthetic characteristics of mulberry seedlings under Na2CO3 stress

The present study analyzed the effects of nitrate nitrogen (NO3--N)on mulberry seedlings growth and photosynthetic characteristics under the alkaline salts (Na2CO3) stress by using solution culture method. Under Na2CO3 stress, stomatal limitation of mulberry seedlings decreased with the increase of NO3--N which improved utilization of carbon dioxide in mesophyll cells in leaves, significantly reduced damages of salt stress on mulberry seedlings, and promoted accumulation of shoot and root biomass. The NO3--N improved actual photochemical efficiency (ФPSⅡ) and electron transfer rate (ETR) of mulberry seedlings, alleviated reduction of PSⅡphotochemical efficiency (Fv/Fm), and reduced the photo inhibition degree of mulberry seedlings leaves under Na2CO3 stress. The increase in NO3--N also reduced the proportion of invalid forms of heat energy dissipation in mulberry seedling leaves under Na2CO3 stress which was useful for leaves to absorbe more lights for photochemical reaction. The synergy between the heat dissipation and xanthophyll cycle effectively protected the normal physiological function of PSⅡ and improved light utilization capacity of the leaves. The NO3--N concentration of 12.5 mmol·L-1 treatment was greater than other concentrations. Therefore, the increase in NO3--N can improve leaves light use efficiency and biomass of mulberry seedling under Na2CO3 stress.