Dynamic characteristics of K, Ca and Mg uptake by litchi as affected by temperature and nitrogen form

Abstract: 【Objective】K, Ca and Mg uptake by litchi under varied temperatures and N forms was investigated, aiming to provide references by selecting suitable N source and K, Ca and Mg nutrient com-binations for litchi in different seasons or phenological stages.【Methods】A hydroponic experiment was conducted using litchi seedlings of cultivar Heiye. The designed growth temperatures were 10, 15, 20, 25, 30 and 35℃, and the supplied N forms included nitrate, 1/2 nitrate + 1/2 ammonium, and ammoni-um. K, Ca and Mg contents in the nutrient solution were measured, and the uptake kinetic parameters of K, Ca and Mg nutrients were determined.【Results】Except that the interaction between temperature and nitrogen nutrition had no significant effect on affinity (Am) of Ca2+ absorbed by litchi, temperature, nitro-gen form and their interaction had significant effects on the absorption of K+, Ca2+ and Mg2+ (p < 0.05).Under the conditions of nitrate and 1/2 nitrate + 1/2 ammonium, the kinetic parameters of litchi on K+fluctuated with temperature increased, while under ammonium nitrogen treatment, the kinetic parame-ters did not change significantly as temperature increased. The maximum absorption rate (Imax) of K+ by litchi at 10, 15 and 30 ℃ was found in the treatment of 1/2 nitrate + 1/2 ammonium, which had a signifi-cantly higher Imax of K+ than the other two treatments. Under the ammonium treatment at 10 and 15 ℃, Imax was significantly higher than under nitrate treatment, but the opposite was found at 30 ℃. There was no significant difference in Imax among the three nitrogen treatments at the other temperatures. Un-der ammonium treatment, the Am of K+ absorbed by litchi always had the maximum value at different temperatures. At 15 and 30 ℃, the Am in the treatment of 1/2 nitrate + 1/2 ammonium was greater than that in the nitrate treatment. However, that in the nitrate treatment was larger at 25 ℃. Under different temperatures, ion compensation concentrations (Cmin) of K+ uptake by litchi was always the highest un-der the nitrate treatment, with the exception of the lowest value in the 1/2 nitrate + 1/2 ammonium treatment at 15 ℃. At 10, 15 and 25 ℃, the Imax of Ca2+ was in the order of nitrate < 1/2 nitrate + 1/2 ammoni-um < ammonium. When the temperature was 20 and 35 ℃, the nitrate treatment was significantly high-er than the other two treatments, and at 35 ℃, the Imax in the 1/2 nitrate + 1/2 ammonium treatment was significantly higher than that in the ammonium treatment. The Am of Ca2 + absorbed by litchi decreased first and then increased with the increase of temperature, and that in the nitrate treatment at 15-35 ℃ was significantly lower than that in the 1/2 nitrate + 1/2 ammonium treatment, and significantly or slightly lower than that in the ammonium treatment. With the increase in temperature, the change pat-tern of Cmin for Ca2+ under different treatments were opposite to that of Am. Under different nutrient treat-ments, the kinetic parameters of Mg2+ fluctuated and changed with temperature increase. At 10 ℃, Imax and Am of Mg 2+ were the highest and Cmin was the lowest, and at 35 ℃ Am was the highest and Cmin was the lowest. At 25 ℃, the ammonium treatment had the largest Imax.【Conclusion】Both temperature and nitrogen form can significantly affect the K, Ca and Mg uptake by litchi. The combination of ammoni-um and nitrate was more beneficial to the absorption of K, Ca and Mg by litchi than the use of single form of nitrogen during the period of autumn shoot growth and fruit expansion period. Calcium and magnesium fertilizers can be sprayed to supplement Ca and Mg nutrients for litchi after autumn shoot maturation and before anthesis.