Mitigating Effects of Topdressing Potassium Fertilization on Photosynthesis, Tissue Structure, and Chemical Component of Waterlogged Tobacco Leaves

Purpose To investigate the effects of field waterlogged on the photosynthetic characteristics, tissue structure, and chemical component of flue-cured tobacco leaves, as well as the mitigating effects of topdressing potassium fertilization, and to analyze the physiological mechanisms.

Methods Using a movable simulated micro-zone device with Yunyan 87, K326, and Honghuadajinyuan as materials, treatments including control (CK), waterlogging (T₁), and waterlogging+topdressing potassium fertilizer (T₂) were established. The photosynthetic parameters, leaf micro-structure, and post-curing chemical component of flue-cured tobacco in the late growth stage were systematically measured, and correlation analysis was conducted.

Results 1) Waterlogging stress significantly inhibited photosynthesis, disrupted the orderliness of palisade tissue arrangement, and reduced the sugar-nicotine ratio (except the middle leaves of K326). 2) Topdressing potassium fertilizer resulted in significant mitigating effects, among which the photosynthetic capacity of the upper leaves of Honghuadajinyuan was most significantly restored, with an average increase of 53.63% in four photosynthetic indicators compared to T₁ treatment; the thickness of leaf palisade tissue increased in various varieties, and the cell arrangement returned to a tight and orderly state, among which the thickness of leaf palisade tissue in the middle leaves of Yunyan 87 significantly increased by 29.08%. Topdressing potassium fertilizer effectively promoted the balance of carbon and nitrogen metabolism, causing the sugar-nicotine ratio of the upper leaves of Honghuadajinyuan and the middle leaves of K326 to be adjusted back to a suitable range of 8-12. 3) Correlation analysis showed that potassium content of leaves was extremely significantly positively correlated with net photosynthetic rate, thickness of palisade tissue, and total sugar content.

Conclusion Topdressing potassium fertilizer can significantly alleviate the photosynthetic inhibition caused by waterlogging and improve the coordination of chemical component in tobacco leaves by repairing the leaf palisade tissue structure and maintaining stomatal function. Among different varieties, Honghuadajinyuan is most sensitive to waterlogging stress and has the most severe response to potassium fertilizer.