Absorption and Distribution of ¹⁵N by Divided Tomato Roots; Part Immersed in a Nutrient Solution and Part in a Humid Atmosphere

Abstract

Absorption and distribution of ¹⁵N by divided tomato root, part immersed in a nutrient solution versus the other part in a humid atmosphere, were composed. When the seedlings had six fully expanded leaves, equal concentrations of K¹⁵NO₃ solution were administered simultaneously to the nutrient solution or the saturated, humid atmosphere. At the end of 72-hr exposure to ¹⁵N, the roots and the rest of the plants were analyzed. On a separate group of plants, the respiration rates of roots in the two root zones were determined. Dry weight, the percent of dry matter and nitrogen content, and nitrogen concentration were significantly higher in roots in the humid atmosphere than those in the nutrient solution. Respiration and ¹⁵N absorption rates were faster in roots in the nutrient solution than those in the humid atmosphere. Roots in the humid atmosphere exported less ¹⁵N to other parts of the plant than did roots in the solution; the former retained more of ¹⁵N that they absorbed and imported more ¹⁵N. In the case where the root system is split so that part immersed in the nutrient solution and the rest in the humid atmosphere, roots in the solution absorbed and supplied nitrogen more efficiently than did roots in the humid atmosphere. The large accumulation of dry matter by roots in the humid atmosphere may increase nitrogen absorption, even though the efficiency is low.