High potassium to magnesium ratio affected the growth and magnesium uptake of three tomato (Solanum lycopersicum L.) cultivars

Potassium (K) and magnesium (Mg) levels and their balances are two factors affecting the growth of plant. However, the responses of different crop cultivars to K/Mg ratios are less clear. This study was aimed at assessing the different responses of tomato (Solanum Lycopersicum L.) cultivars to the different K/Mg supply ratios. Three tomato cultivars (Zhongza 9 (ZZ), Gailiangmaofen (MF), and Jinpengchaoguan (JP)) were grown in pots with three different K+/Mg2+ ratios (4:0, 4:1 and 8: 1, represented by K/Mg 4: 0, K/Mg 4: 1, and K/Mg 8: 1, respectively). Compared with K/Mg 4: 1 treatment, the leaf chlorophyll content, net photosynthetic rate, and total biomass of tomato seedlings under K/Mg 4: 0 treatments were decreased by 69.7, 89.1, and 53.1%, respectively. The Mg deficiency symptoms were observed when the Mg content in shoot became lower than 4 mg g(-1) DW. Compared with K/Mg 4:1 treatment, total biomass of tomato seedlings of K/Mg 8:1 treatment was decreased by 21.6%; the shoot and root Mg contents were decreased by 10.4 and 21.8%, respectively; and Mg uptake of tomato was reduced by 34.1%. There were significant differences in biomass and Mg uptake for the three cultivars between the different K+/Mg2+ treatments. The Mg uptake of the three different cultivars ranked as ZZ>JP>MF under Mg deficiency and high K condition. In conclusion, the growth and Mg uptake and allocation of tomato were influenced significantly by imbalance K and Mg supply. JP and ZZ were the cultivars with the highest efficiency in Mg uptake.