ABSTRACT
The coordination/trade-off among below-ground strategies for phosphorus (P) acquisition, including root morphology, carboxylate exudation and colonisation by arbuscular mycorrhizal fungi (AMF), is not well understood. This is the first study investigating the relationships between root nodulation, morphology, carboxylates and colonisation by an indigenous community of AMF under varying P levels and source. Two chickpea genotypes with contrasting amounts of rhizosheath carboxylates were grown in pots at six P levels (from 0 to 160 µg g-1 ) as KH2 PO4 (KP, highly soluble) or FePO4 (FeP, sparingly soluble), with or without AMF (±AMF) treatment. Under both FeP and KP, the presence of AMF inhibited shoot growth and shoot branching, decreased total root length and specific root length, increased mean root diameter and root tissue density and reduced carboxylates. However, the role of AMF in acquiring P differed between the two P sources, with the enhanced P acquisition under FeP while not under KP. Co-inoculation of AMF and rhizobia enhanced nodulation under FeP, but not under KP. Our results suggest that the effects of AMF on shoot branching were mediated by cytokinins as the reduced shoot branching in FeP40 and KP40 under +AMF relative to -AMF coincided with a decreased concentration of cytokinins in xylem sap for both genotypes.
