硝态氮对Na_2CO_3胁迫下桑树幼苗生长和光合特性的影响

Effects of NO3--N on growth and photosynthetic characteristics of mulberry seedlings under Na_2CO_3 stress

利用溶液培养法在碱性盐(Na2CO3)胁迫下研究了硝态氮(NO3--N)对桑树(Morus alba)幼苗生长和叶片光合特性的影响。结果表明,增加NO3--N降低了Na2CO3胁迫下桑树叶片的气孔限制,改善了叶肉细胞对CO2的利用,提高了光合碳同化能力,明显减轻Na2CO3胁迫对桑树幼苗的盐害,促进了地上部和根系生物量的积累。NO3--N提高了桑树叶片的实际光化学效率(ФPSⅡ)和电子传递速率(ETR),缓解了Na2CO3胁迫下最大光化学效率(Fv/Fm)的降低,减轻了由于Na2CO3胁迫引起的光抑制程度,同时,增加NO3--N降低了Na2CO3胁迫下桑树幼苗叶片以无效热能形式耗散的比例,叶片吸收的光能更多地分配到光化学反应之中,并且通过热耗散和叶黄素循环之间的协同作用有效地保护了光合PSⅡ的生理功能,提高了叶片的光能利用能力。不同NO3--N浓度之间比较,12.5 mmol·L-1的NO3--N处理桑树幼苗比其他浓度处理的效果更好。因此,在Na2CO3胁迫下,增加NO3--N可改善桑树幼苗叶片的光能利用效率,增加桑树的生物产量。

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 PSⅡ photochemical 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- 1treatment 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.