Potassium partitioning and redistribution as a function of K-use efficiency under K deficiency in sweet potato (Ipomoea batatas L.)

Interactions exist between environmental factors and potassium use efficiency (KIUE) in crops, while controversy exists on the relationship between KIUE and other crop characteristics. In field experiments conducted during 2012-2014, genotypes 'Xu28' (high KIUE) and 'Ji22' (low KIUE) were identified and analyzed under conditions of K deficiency (K0) and adequate K supply (K1). Variation in KIUE at different growth years and correlations between KIUE and other parameters were studied in field trials in 2013 and 2014, combined with a greenhouse experiment in 2015. 'Xu28' and 'Ji22' showed a consistent ranking in terms of traits involving K-use efficiency, but marked variations in KIUE were observed between field trials and greenhouse experiments, as well as at different stages of plant development in the field experiments. KIUE exhibited a significant negative correlation with whole-plant K concentration under both field and greenhouse conditions, while KIUE was significantly positively correlated with the potassium harvest index in the field experiments, although no significant correlation was observed between root tuber yield and biomass production. 'Xu28' exhibited faster K concentration declines than did 'Jin22' from plantlet stage to harvest in both the 2014 field experiment and the 2015 greenhouse experiment. In the 2014 field experiment, under K0 conditions, 'Xu28' shoot and root K concentrations declined from plantlet stage to harvest by 178% and 142%, respectively. In contrast, 'Ji22' shoot K concentration declined from plantlet stage to harvest by 86%, while root K concentration remained stable. The percentage of fallen litter K content to whole-plant K content varied from 4.5% ('Ji22' K0) to 8.9% ('Xu28' K1) under greenhouse conditions, and 'Xu28' exhibited significantly higher fallen litter K (as a percentage of the whole plant) than did 'Ji22' under K0 and K1 conditions. The root:shoot ratio of K accumulation at harvest in 'Xu28' was significantly higher than that in 'Ji22' in both the 2014 field experiment and the greenhouse trial. KIUE was positively correlated with whole-plant K concentration at harvest of sweet potato, whereas root tuber yield was not significantly correlated with KIUE. The high-KIUE 'Xu28' had a more optimal partitioning of K at harvest than did the low-KIUE 'Ji22', as well as better K translocation in the shoots and roots at different growth stages, and these traits were of crucial importance for achieving high KIUE.