64. Organic Phosphorus

Organised by Benjamin Turner (Smithsonian Institute) and Hans Lambers (U Western Australia) to be held at University of Western Australia, Perth. First meeting 30 November - 4 December 2009

PARTICIPANTS 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 Jonathan 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

Dec 09>

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).

OBJECTIVES

Four key issues will be addressed:

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.

Literature Cited:
1. Condron, L.M., B.L. Turner, and B.J. Cade-Menun. 2005. The chemistry and dynamics of soil organic phosphorus. pp. 87-121. In J.T. Sims and A.N. Sharpley (eds). Phosphorus: Agriculture and the Environment. ASA-CSSA-SSSA, Madison, Wisconsin, USA.
2. Richardson, A.E., T.S. George, M. Hens, and R.J. Simpson. 2005. Utilization of soil organic phosphorus by higher plants. pp. 165-184. In B.L. Turner, D.S. Baldwin, and E. Frossard (eds) Organic Phosphorus in the Environment. CAB International, Wallingford, UK.
3. Turner, B.L. 2008. Resource partitioning for soil phosphorus: a hypothesis. Journal of Ecology 96:698-702.
4. Lambers, H., J.A. Raven, G.R. Shaver, and S.E. Smith. 2008. Plant nutrient-acquisition strategies change with soil age. Trends in Ecology and Evolution 23:95-103.
5. Leake, J.R. 2002. Organic phosphorus utilisation by mycorrhizal plants and fungi: How much do we really know? In B.A. Whitton and I. Hernandez (eds) Phosphatases in the Environment. Kluwer Academic Press, Dordrecht, Netherlands.
6. Koide, R.T., and Z. Kabir. 2000. Extraradical hyphae of the mycorrhizal fungus Glomus intraradices can hydrolyse organic phosphate. New Phytologist 148:511-517.
7. Joner, E.J., van Aarle, I. M., and Vosatka, M. 2000. Phosphatase activity of extra-radical arbuscular mycorrhizal hyphae: A review. Plant and Soil 226:199-210.
8. Dodd, J.C., C.C. Burton, R.G. Burns, and P. Jeffries. 1987. Phosphatase activity associated with the roots and the rhizosphere of plants infected with vesicular-arbuscular mycorrhizal fungi. New Phytologist 107:163-172.

Last Updated January 2010