Carboxylates in the rhizosphere of canola, wheat, lupins and pulses: their role in P acquisition from sparingly soluble forms
Native Australian soils contain very low amounts of phosphorus. The soils of southwestern Australia are ancient and highly weathered. Consequently, the availability of phosphorus in these soils is too low for cropping purposes, so the application of P is necessary to maintain productivity. When P is applied to soil, typically as soluble superphosphate, it tends to be transformed to increasingly less soluble forms over time. Sparingly soluble forms of soil P are relatively inaccessible to Triticum aestivum; however, many grain legumes have a higher P-acquisition efficiency, allowing them to access pools of soil P that T. aestivum cannot. The P-acquisition efficiency of some grain legumes has been attributed in part to their ability to release large quantities of carboxylates, coupled with the development of cluster roots for species such as Lupinus albus. There are a number of unexplained observations in terms of the P-acquisition efficiency of grain legume species and the way that those species respond to P fertilisation. This PhD project aimed to study carboxylate release from a range of crop species, and investigate its role in variation among species for acquisition of phosphorus from sparingly soluble forms.
This research is important because if we can understand the physiology that allows plants to access forms of phosphorus in soil that are otherwise unavailable, we may in the future be able to develop legume cultivars that can be rotated with very low phosphorus application. Instead they could draw on a store or 'bank' of phosphorus in the soil that has been estimated to be valued at close to $10 billion dollars.