Indigenous arbuscular mycorrhizal (AM) fungi contribute to wheat phosphate uptake in a semi-arid field environment, shown by tracking with radioactive phosphorus

• The contribution of indigenous arbuscular mycorrhizal fungi to phosphate uptake by wheat in a semi-arid agricultural system in southern Australia was tracked with 33P.
• By 67 days AM fungi contributed 6.5–21% of shoot P uptake (equivalent to 0.16 kg P ha−1), despite low AM colonisation.
• Field results were similar to a pot experiment in the same soil.
• AM fungi should not be ignored in wheat P uptake efficiency and pot experiments may be valuable in predicting likely outcomes in the field.

The aim was to determine the quantitative contribution of naturally-occurring arbuscular mycorrhizal (AM) fungi to phosphorus (P) uptake by wheat in the field in a semi-arid, agricultural environment. Findings were compared with a pot experiment in the same soil in order to assess the predictive value of pot experiments. Similar compartmented systems were used in both experiments, to provide radioactive P only to the AM fungal assemblage. Delivery of P to the plants was tracked and the contributions of the AM uptake pathway quantified. AM colonisation from the soil in both experiments was low and variable. A range of colonisation morphologies indicated the presence of several different AM fungi. By 44 d (pot experiment) and 67 d (field experiment) the AM pathway delivered P to all 10 plants in pots and 115/120 plants in the field. The contributions were 3–40% of total P to whole plants in pots and 6.5–21% to shoots in the field, equivalent to means of approximately 0.48 and 0.16 kg P ha−1, respectively (minimum estimates, see text). There was no significant relationship between % root length colonised and amount of P delivered via the AM pathway in either experiment. Even with low AM colonisation, the natural assemblage of indigenous AM fungi made a significant contribution to P uptake by wheat, a plant that is often regarded not to benefit from AM colonisation. We conclude that it is feasible to use compartmented systems in the field to estimate the quantitative contribution of AM fungi to P uptake by plants and that it is unwise to ignore the AM contribution in research aimed to understand mechanisms potentially contributing to P uptake efficiency.