Sodium-potassium synergism in Theobroma cacao: Stimulation of photosynthesis, water-use efficiency and mineral nutrition

Abstract

In ecological setting, sodium (Na+) can be beneficial or toxic, depending on plant species and the Na+ level in the soil. While its effects are more frequently studied at high saline levels, Na+ has also been shown to be of potential benefit to some species at lower levels of supply, especially in C4 species. Here, clonal plants of the major tropical C3 crop Theobroma cacao (cacao) were grown in soil where potassium (K+) was partially replaced (at six levels, up to 50% replacement) by Na+, at two concentrations (2.5 and 4.0 mmolc dm-3). At both concentrations, net photosynthesis per unit leaf area (A) increased more than twofold with increasing substitution of K+ by Na+. Concomitantly, insta..