Potassium (K+) is an essential mineral element affecting plant growth and development. The aim of this study was to investigate the physiological response to K+ deficiency in three sweet potato (Ipomoea batatas [L.] Lam.) cultivars with differing K+ utilization efficiencies (KUE). The effects on plant growth status, physiological characteristics, leaf ultrastructure, and photosynthesis were examined. The results showed that K+ deficiency significantly decreased total biomass productivity, root yield, photosynthetic efficiency, and chlorophyll (Chl) content, while increased leaf sucrose and proline content of the three cultivars. K+ deficiency caused acute damage to chloroplast ultrastructure associated with leaf Chl biosynthesis and photosynthate accumulation, and also disturbed the protective enzymes involved in the antioxidative defense system. Compared with the other two cultivars, Xushu32 had higher root yield and better growth performance under K+ deficiency, which was mainly attributed to its high KUE and greater carbohydrate conversion and net photosynthetic efficiency. As a whole, these data suggest that greater tolerance to K+ deficiency among sweet potato genotypes is associated to the capability to mount a stronger physiological stress response during growth.
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