Carboxylates in the rhizosphere of chickpea (Cicer arietinum) in relation to P acquisition

[Truncated abstract] The highly weathered, phosphorus-fixing soils of Western Australia require large amounts of P fertiliser to produce acceptable crop yields. Chickpea (Cicer arietinum L.) is an important leguminous crop that is increasingly used in rotations with wheat (Triticum aestivum L.), Western Australia’s major crop. Chickpea and a range of other species exude P-mobilising carboxylates into the rhizosphere. Plants that exude carboxylates may need less P fertiliser or may use P in the soil that is unavailable to other plants. There is a wealth of information about P mobilisation and carboxylate exudation by white lupin; in contrast, research on carboxylate exudation by chickpea is fairly limited. The major aim of this PhD research project was to investigate the relationships between exudation of carboxylates and soil and plant P status for chickpea ... In conclusion, whereas carboxylate exudation of plants such as white lupin is clearly targeted at P acquisition, chickpea showed constitutive carboxylate exudation mainly of malonate into the rhizosphere in a series of experiments, each with a different design. Unlike white lupin, chickpea forms associations with mycorrhizal fungi that may improve plant P status. Some of the functions of constitutive carboxylate exudation by chickpea may include P acquisition and deterring microorganisms, but the exact reasons and mechanisms remain unresolved.