Root-released organic acids and phosphorus uptake of two barley cultivars in laboratory and field experiments

A major portion of phosphorus (P) applied as fertilizers is bound in soils as P compounds of variable adsorption strength, reducing the effectiveness of P fertilization. Plant genotypes equipped with mechanisms for utilizing the adsorbed P more efficiently can, therefore, enhance the effectiveness o f P fertilization. Such genotypes will also enrich plant gene pools for fur ther analysis and upgrading of P efficiency by selection and breeding. We s tudied the variation and the mechanisms of P uptake of two winter barley (H ordeum vulgare L.) cultivars Marinka and Senate (parents of existing 200 ha ploid progeny lines), by laboratory and field experiments. After cultivatio n in nutrient solution for 21 days, Marinka produced more roots than Senate , but similar amounts of dry shoots of lower P content (Marinka 3.4 +/- 0.4 mg g(-1), Senate 4.9 +/- 0.6 mg g(-1)). The total P uptake per plant did n ot differ between the cultivars. Marinka retained more P in roots as indica ted by the higher concentration of P in the roots (Marinka 3.9 +/- 0.3 mg g (-1) and Senate 3.0 +/- 0.4 mg g(-1)). In sterile nutrient solution culture , the cultivars differed mainly in release of organic acids from the roots, with Marinka releasing three times more citric acid and nearly two times m ore acetic acid than Senate. The cultivars had similar root hair lengths an d they did not differ (P > 0.05) in depletion of available soil P fraction (extracted with 0.5 M NaHCO3) in the rhizosphere. Marinka absorbed nearly t wice as much P from the strongly adsorbed soil P fraction (extracted with 0 .1M NaOH). Also under field conditions, Marinka absorbed more P and produce d more shoot dry matter. The higher P uptake by Marinka than Senate can be attributed to its ability to acquire P from strongly adsorbed soil P by rel easing more organic acids, especially citric acid, from its roots. (C) 2000 Elsevier Science B.V. All rights reserved.