Carboxylate composition of root exniates and the ability of wheat, canola and different lupin and pulse species to use phosphorus from soluble and sparingly soluble phosphorus sources

摘要

The exudation of carboxylates from roots into soil mobilises sorbed phosphorus (P) that is unavailable for plants that do not release carboxylates. The study of the release of these compounds offers considerable potential for increasing Australian dryland cropping efficiency with regard to P use. We screened for the presence of carboxylates in the rhizosphere of Brassica napus, Cicer arietinum, Lens culinaris, Lupinus albus, L. angustifolius, L. atlanticus, L. cosentinii, L. luteus, L. mutabilis, L. pilosus, Pisum sativum, Triticum aestivum and Vicia faha grown in sand at two levels of P. Malic and citric acid were dominant exudates for all species, with the exception of L. culinaris and C. arietinum, which exuded primarily malonic acid. We studied the effect of P supply as soluble KH_2PO_4, compared with sparingly soluble AlPO_4, FePO_4, or Ca_5OH(PO_4)_3 on biomass accumulation and rhizosphere carboxylates in T. aestivum, B. napus, C. arietinum, P. sativum, L. albus, L. angustifolius and L. cosentinii. There were clear biomass differences without visual signs of aluminium or P toxicity, but no simple relationships between biomass accumulation, root mass ratio, rhizosphere pH and carboxylate release. Total carboxylate release by species varied depending on the form of P supplied, but composition was affected only by soluble P supply. The lack of a relationship between P uptake and rhizosphere chemistry suggests that root exudates have different effects in species with different root morphology.