RC20. The contribution of soil organic phosphorus to plant nutrition

30th November 2009, at University of Western Australia, Perth.

SPEAKERS INCLUDE Benjamin L. Turner (co-leader) - Smithsonian Tropical Research Institute (Republic of Panama) - ecological significance of soil organic phosphorus Hans Lambers (co-leader) - U Western Australia - plant physiological responses to extreme phosphorus deficiency Leo Condron - Lincoln U (New Zealand) - soil organic phosphorus dynamics in natural and agricultural ecosystems Michael Cramer - U Cape Town (South Africa) - rhizosphere nutrient interactions and proteiod roots Jonathon Leake - U Sheffield (UK) - phosphatase and the utilization of soil organic phosphorus by mycorrhizal fungi Alan Richardson - CSIRO Plant Industry - plant acquisition of soil organic phosphorus, heterotrophic soil microbes and phosphorus acquisition, the development of transgenic plants that secrete phytase Sally Smith - U Adelaide - mycorrhizal symbiosis and nutrient acquisition

On Monday 30th November there will be an intensive 1-day research course offered, open to interested researchers and ECR and HDR.

The purpose of the remainder of the week for working group participants will be to address the following four key issues:

1. The chemical nature and dynamics of soil organic phosphorus in terrestrial ecosystems.
2. The turnover of soil organic phosphorus by heterotrophic microbes.
3. The role of mycorrhizas in the acquisition of soil organic phosphorus.
4. The ecological significance of soil organic phosphorus acquisition by plants.

Background
Organic phosphorus is abundant in soils and can be utilized by plants through a variety of mechanisms, including association with mycorrhizal fungi, promotion of specific non-symbiotic microorganisms in the rhizosphere, and release of phosphatase enzymes by roots (1). Yet despite the widespread extent of phosphorus limitation in terrestrial ecosystems, notably in Australia, the contribution of organic phosphorus to plant nutrition is unclear (2). As a result, the focus of research remains on inorganic forms of phosphorus, which restricts our understanding of the nutrient status of ecosystems and mechanisms underlying the distribution of plants within them (3).

There is no evidence of direct uptake of organic phosphorus by plants, so it is assumed that organic phosphorus must always be hydrolyzed by phosphatase enzymes prior to uptake of inorganic phosphate. Sources of phosphatase include plant roots, mycorrhizas, and heterotrophic soil microbes, but their contribution to the mineralisation of soil organic phosphorus and subsequent uptake of phosphate by plants is poorly understood. Associations with mycorrhizal fungi are clearly important (4): ericoid and ectomycorrhizas can access organic nutrients, yet research on such fungi is usually restricted to the acquisition of organic nitrogen rather than organic phosphorus (5). Arbuscular mycorrhizal fungi, which form associations with the majority of species of land plants, are often assumed to access only inorganic phosphate, although there is some evidence that they can also access organic phosphorus (6). Critically, the extent to which plants rely on mycorrhizas to access organic phosphorus remains unclear (7) – the release of phosphatase enzymes by roots is a ubiquitous response to phosphorus deficiency (8), while plants growing on the most phosphorus-deficient soils do not typically form associations with mycorrhizal fungi (4).

Last Updated July 2009