The carboxylate composition of rhizosheath and root exudates from twelve species of grassland and crop legumes with special reference to the occurrence of citramalate
Low-molecular-weight organic anions (carboxylates) influence rhizosphere processes and may enhance plant phosphorus acquisition. We examined the root exudate profile of a range of pasture and grain legumes and focused on the little-investigated carboxylate, citramalate.
Twelve species of pasture legumes and herbs, including four Lotus spp. and two crop legumes, Cicer arietinum and Lupinus albus, were grown in a glasshouse for six weeks. The composition and amounts of carboxylates were measured in rhizosheath soil as well as in root exudates from roots washed free of their rhizosheath.
Citrate and malate were found in the rhizosheath of all species. However, citramalate was present in the rhizosheath of only Lotus species (10–82% of total exuded carboxylates). Cicer arietinum had the largest amount of carboxylates in its rhizosheath and fastest rate of carboxylate exudation into the trap solution.
Citrate and malate were found in the rhizosheath of all species in this study, but citramalate was only found in the root exudates and rhizosheath of Lotus spp. Further investigation into the role of citramalate in Lotus spp. is merited.
KeywordsCitrate Exudation Lotus Organic acids Phosphorus Rhizosheath
This project was funded by Meat and Livestock Australia and Australian Wool Innovation Limited through the project “Phosphorus-efficient legume pasture systems” (B.PUE.0104). The authors acknowledge the facilities, and the scientific and technical assistance of the Australian Microscopy & Microanalysis Research Facility at the Centre for Microscopy, Characterisation & Analysis, The University of Western Australia, a facility funded by the University, and State and Commonwealth Governments. Megan Ryan was funded by an ARC Future Fellowship (FT140100103).
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