Effects of the supply of K, Ca, and Mg on the absorption and assimilation of ammonium- and nitrate-nitrogen in tomato plants

Abstract

Abstract Forty-two-day-old tomato (Lycopersicon esculentum Mill. cv. Fukuju Nigo) plants were treated with complete, K-free, Ca-limited, and Mg-free nutrient solutions for 10 days using 2 mM NH4NO3 as the N source, which was replaced with 4 niM 15NH4Cl or Na15NO3 for the following 2 days to examine the absorption, translocation, and assimilation of inorganic N in relation to the supply of K, Ca, and Mg. The changes in the leaf nitrate reductase activity (NRA) were examined in tomato plants grown in nutrient solutions in which the form of N source and the supply of K and Ca were varied. Leaf contents of K, Ca, and Mg decreased to 38, 45, and 67% of those of the control plants in the low-K plants, the low-Ca plants and the low-Mg plants, respectively. Tomato plants absorbed NO3-N more efficiently than NH4-N. A larger amount of labelled N from NO3-N than from NH4-N was translocated to shoot. Removal of K from the nutrient solution slightly enhanced the absorption of NH4-N, but suppressed the absorption, tran...