Sodium and Potassium Absorption and Distribution in Relation to Growth and Internal Potassium Use Efficiency of K-efficient and -inefficient rice genotypes

A pot experiment with two rice (Oriza sativa L.) genotypes differing in internal potassium use efficiency (IKUE) was conducted under different sodium (Na) and potassium (K) levels. Adding NaCl at a proper level enhanced rice vegetative growth and increased grain yield and IKUE under low potassium. Addition of higher rate of NaCl had a negative effect on the growth of the K-efficient rice genotype, but did not for the K-inefficient genotype. Under low-K stress, higher NaCl decreased IKUE of the K-efficient rice genotype but increased IKUE for the K-inefficient genotype. At tillering stage and under low-K stress, adding NaCl increased K and Na contents and decreased the ratio of K/Na for both genotypes. At harvesting stage under low-K stress, adding NaCl increased K and Na contents and K/Na ratio for the K-efficient genotype but decreased the K/Na ratio for the K-inefficient genotype. The accumulated Na was mostly deposited in the roots and sheaths. At tillering stage, the K and Na contents and the K/Na ratios in different parts for both genotypes decreased in the following sequence: K+ in sheaths > K+ in blades > K+ in roots; Na+ in roots > Na+ in sheaths > Na+ in blades; and K/Na in sheaths 》 K/Na in roots. The K-efficient genotype had a lower K/Na ratio in roots and sheaths than the K-inefficient genotype under low-K stress. At harvesting stage, K and Na contents in grains were not affected, whereas K/Na ratio in the rice straws was increased for the K-efficient genotype but decreased for the K-inefficient genotype by Na addition. However, this was not the case under K sufficient condition.