Promising look at soil phosphorus

THE INTERNATIONAL Symposium on Phosphorus Cycling in the Soil-Plant Continuum, held last year in Beijing, China, shed light on the factors that influence the availability of phosphorus in soil and explored ways to exploit organic and mineral phosphorus. Such study will lead to new opportunities for managing soil phosphorus and for developing plants that are more phosphorus-efficient.

The meeting was jointly hosted by the ChinaAgricultural University, the Chinese Academy of Sciences, the National Nature Science Foundation of China, the University of Western Australia and AusAID. The meeting was particularly valuable in that it brought together researchers working on various aspects of phosphorus in both plants and soils. Among a diverse range of topics relating to soil chemistry and phosphorus availability were discussions on mechanisms of phosphorus acquisition by plants and on the genetics and molecular biology of plant phosphorus nutrition.

Representatives from leading international laboratories participated and Australia, in particular, was well represented in view of the important role that phosphorus fertiliser plays in Australian agriculture. The GRDC provided support for several Australian scientists to attend this meeting.

A focus of the meeting was to understand factors that influence the availability of phosphorus in soil. In particular, a number of papers highlighted the need to better understand the significance of phosphorus cycling from accumulated mineral and organic forms of P.

Alan Richardson from CSIRO Plant Industry reported on research that showed plants genetically modified to secrete a phytase enzyme were able to use organic forms of phosphorus that are otherwise unavailable for plants. This research opens up the exciting possibility of engineering crop plants to enable better use of organic phosphorus accumulated in Australian soils.

A recurrent theme at the meeting was the importance of organic acid exudation by plant roots as a mechanism for obtaining phosphorus from soils and for conferring aluminium tolerance, a problem with acid soils. There is now considerable evidence from many laboratories demonstrating both of these beneficial effects of organic acids for a range of plant species.

A challenge now is to be able to use plants that secrete organic acids to improve the P nutrition of cropping systems and, from a biotechnology perspective, to develop cultivars better able to exude organic acids to improve both their phosphorus nutrition and aluminium tolerance. For instance, Albus lupin naturally forms specialised roots that exude large amounts of citrate, which allows the plant to acquire phosphorus from soils that is unavailable to many other species.

There were also excellent presentations on new analytical methods to allow a better understanding of the behaviour of phosphorus in soils.

The meeting provided an opportunity to make contact with bright young scientists in the field of phosphorus nutrition. Two of these scientists are now employed in laboratories at CSIRO Plant Industry on projects supported by the GRDC and Australian Wool Innovation Pty Ltd. The phosphorus symposium played a large part in attracting these outstanding young researchers to Australia.

'Dr Delhaize, a plant physiologist at CSIRO Plant Industry, attended the Chinese meeting with support from growers and the Federal Government through the GRDC.

Program 6 Contact: Dr Manny Delhaize 02 6246 5047 email