Potassium internal use efficiency relative to growth vigor, potassium distribution, and carbohydrate allocation in rice genotypes

Potassium (K) deficiency in soils is widespread and has become one of the most nutritional limiting factors for increasing rice yield in China and Asia. Improving K use efficiency by exploiting genetic potential largely depends on understanding physiological and genetic mechanisms underlying K efficiency in lowland rice. In this study, the K internal use efficiency (KIUE) at low K supply relative to K accumulation and distribution, tillering and grain Filling rates, dry matter accumulation and allocation were examined under field conditions. The relative K concentrations in upper and lower leaves at booting and grain filling stages decreased with decreasing K internal use efficiency among the rice genotypes, indicating that K-efficient genotypes had greater K translocation ability than the K-inefficient genotypes at low K. The KlUE in biomass production at seedling and tillering stages was closely and positively correlated with the KIUE in grain production at the harvest stage. Significant positive correlations were noted between the KIUE at low K and the relative dry matter yield at the tillering stage and the harvest index among the rice genotypes. The K-efficient genotypes had a greater relative tillering rate during the tillering stage and a greater relative grain filling rate at the late grain filling stage, as compared with the inefficient genotypes. The relative net photosynthetic rate in the upper, and especially in the lower leaves was much lower in the K-inefficient genotypes than in the efficient ones at the grain filling stage, which may partly be due to the fact that the efficient genotype could maintain greater stomatal conductance and ribulose diphosphate carboxylase (RuBPcase) activity in functioning leaves under low K. The results indicate that (i) the K internal use efficiency could be an important index for measuring rice tolerance to low K stress, and (ii) K internal use efficiency is closely associated with efficient translocation and distribution of both K and carbohydrate within rice plants.