Ability of various water-insoluble fertilizers to supply available phosphorus in hydroponics to plant species with diverse phosphorus-acquisition efficiency: Involvement of organic acid accumulation in plant tissues and root exudates

Previous studies describe the suitability of a new type of phosphorus (P) fertilizer, called rhizosphere-controlled fertilizer (RCF), to supply available P to plants while reducing soil phosphorus fixation. In order to explore the involvement of organic acid root exudation in P uptake from RCF, we investigated the relationship between shoot and root P concentrations, and the concentration of the main polycarboxylic organic acids in roots, shoots, and plant exudates Plant species with different P-acquisition efficiency (low maize, medium chickpea; high. lupin) were grown in hydroponics with three different P fertilizers The water-insoluble P fraction of RCF (RCF), Phospal, a slow-release source of phosphate composed of calcium and aluminum phosphates (PH), monopotassiumphosphate (KP), and a control treatment without P (P-) RCF was as efficient as KP in supplying P to plants in the case of chickpea and lupin, and slightly less efficient than KP in maize However, P from PH was not available for maize and less available compared to KP and RCF in chickpea and lupin This variation reflects the different efficiencies in P acquisition for the three plant species Except in the case of maize, plants receiving KP presented the lowest concentration of organic acids in roots and exudates, while those plants suffering severe P deficiency (P- and PH) showed the highest organic acid concentration However, RCF had a high concentration of organic acids in roots and exudates, as well as a high P concentration in the shoot indicating that P uptake from RCF is enhanced due to root release and action of specific organic acids