The role of arbuscular mycorrhizal fungi in uptake by pasture legumes of phosphorus provided as a pulse

[Truncated] In the southern Australian cropping zone, large areas of land contain legume-basedpastures; these provide feed for livestock and nitrogen for following crops. Annualpastures, especially of Trifolium subterraneum (subterranean clover), are widely sownin Mediterranean climates around the globe and particularly in southern Australia.However, the predominance of annual pastures and crops in south-western Australia hascaused problems, including dryland salinisation. Consequently, the development ofnovel perennial pasture plants, including Australian natives, has been a research priorityover the past 15 years.

Phosphorus fertiliser is a common input to farms in southern Australia and its use hasmuch increased soil P concentrations. However, rock phosphate is a non-renewableresource and it is now more important to use it efficiently. Forming a symbiosis witharbuscular mycorrhizal fungi (AMF) is an important means for plants to enhance their Puptake, primarily because their external hyphae are able to explore a greater volume ofsoil than plant roots can alone. Mycorrhizal experiments are usually conducted underconstant or decreasing P levels due to plant P uptake. However, few studies havefocused on the response of colonised plants to a pulse of P as may occur under fieldconditions such as when the first winter rain falls after a hot dry summer or when Pfertilisers are applied to growing plants. To my knowledge, this study is the first toconcentrate on the role of AMF in plant P uptake from a P pulse. Care was taken toensure that results were relevant to field conditions and therefore the soil used in allexperiments was a field soil with a moderate concentration of plant available P (18 mgkg^-1), as is common in the cropping areas of Western Australia.