Exudation of low molecular weight organic acids by Lupinus albus L., Lupinus angustifolius L. and Lupinus luteus L. as affected by phosphorus supply

摘要

The objective of this investigation was to study the influence of P fertilizer application on the quality and quantity of organic acid exuded by six cultivars of three lupin species: Lupinus albus L. ( cultivars Minori and Nelly), Lupinus angustifolius L. ( cultivars Borweta and Bordako) and Lupinus luteus L. ( cultivars Borsaja and Borselfa). We also investigated the influence of the exudate collection medium (deionized water, 0.05 mM CaCl2 solution) on the composition and the intensity of exuded organic acids in L. albus (cultivar Minori). Plants were grown in quartz sand with (+ P) and without ( - P) fertilization for 21 days. The plants were removed carefully from the sand, the roots washed, and then allowed to release exudates into deionized water or 0.05 mM CaCl2 solution twice for two hours or twice for four hours. Root length was measured. Root morphology was also reported. The results show that L. albus formed dense root clusters known as proteoid roots. The proteoid root formation was greatest under P deficiency conditions. A similar root system was observed in yellow lupin but this was less dense than in white lupin. Blue lupin did not form root clusters. Regardless of P nutrition, eight organic acids ( citric, 2-oxoglutaric, malic, succinic, lactic, formic, acetic and fumaric acids) were identified in the collection solution of all six cultivars. The collection medium did not affect the amount and composition of released carboxylates within four hours. Exudates collected in CaCl2 solution over an 8-hour period contained citric, malic and succinic acids as the most important organic acids. L. angustifolius showed the greatest average carboxylate efflux. Cultivated under P deficiency conditions, five cultivars increased their citrate exudation rate ( on average, 67% for L. albus, 37% for L. angustifolius and 72% for L. luteus).