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The aim of this study was to investigate carbohydrate metabolism in rice seedlings subjected to salt-alkaline stress. Two relatively salt-alkaline tolerant (Changbai 9) and sensitive (Jinongda 138) rice cultivars, grown hydroponically, were subjected to salt-alkaline stress via 50 mM of salt-alkaline solution. The carbohydrate content and the activities of metabolism-related enzymes in the leaves and roots were investigated. The results showed that the contents of sucrose, fructose, and glucose in the leaves and roots increased under salt-alkaline stress. Starch content increased in the leaves but decreased in the roots under salt-alkaline stress. The activities of sucrose-phosphate synthase, sucrose synthase, amylase, and ADP-glucose pyrophosphorylase increased whereas the activities of neutral invertase and acid invertase decreased in the leaves under salt-alkaline stress. The activities of sucrose-phosphate synthase, sucrose synthase, amylase, neutral invertase, and acid invertase increased in the roots under salt-alkaline stress. In conclusion, salt-alkaline stress caused the accumulation of photosynthetic assimilates in the leaves and decreased assimilation export to the roots.

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Aims salinisation severely limits crop growth and yield. In recent years, the effect of nitrogen fertilisation and different management practices on the mitigation of saline-sodic stress in crops has been less studied. Therefore, we conducted a three-year field experiment in Jilin Province, China, to investigate the effects of combined straw and nitrogen fertilizer application on the physiological and photosynthetic characteristics of rice in saline-sodic paddy fields. Methods The experiment was designed as a split-zone trial, with straw (S) as the main zone and nitrogen fertilizer (N) as the secondary zone. The amount of straw returned was 0 t ha-1 (B) and 7 t ha-1 (T). Nitrogen treatments of 0, 150, 250 and 350 kg ha-1 were recorded as N0, N1, N2 and N3, and each treatment was repeated three times. Results Straw combined with nitrogen fertilizer can effectively reduce the Na+/K+ value, malondialdehyde content and relative electric leakage of rice leaves in salt-alkali soil, and ensure the integrity of cell membrane. At the same time, the leaf water potential, relative water content and chlorophyll content were increased, which promoted rice photosynthesis and improved rice yield. In addition, it was found that straw combined with nitrogen fertilizer had the greatest positive effect on rice yield at 250kg ha-1. Conclusions Straw combined with nitrogen fertilizer can improve the physiological and photosynthetic characteristics of rice in saline-alkali paddy field and provide a theoretical basis for rice yield increase in this area