Fig. 1

Effect of grafting combination and K⁺ supply level on whole plant K⁺ uptake (I) and transfer efficiency of K⁺ to the leaves (II). The tobacco graft combinations included the ungrafted tobacco W (Wufeng No.2) and Y (Yunyan 87), and grafted tobacco Y/W (Y grafted onto W) and W/Y (W grafted onto Y). Different uppercase letters denote significant differences (P < 0.05) under normal potassium levels (5 mmol L^− 1) and lowercase letters indicate significant differences (P < 0.05) under starvation (0.5 mmol L^− 1)