Mycorrhizal growth and phosphorus responses of tomato differ with source but not application rate of phosphorus fertilisers

Phosphorus (P) can be added to the soil from various sources (e.g., chemical fertilisers and organic materials), and P fertilisation affects mycorrhizal colonisation and function in plants. While arbuscular mycorrhizal symbiosis is an integral part of most crop plants, there is a gap in understanding mycorrhizal growth and nutrition responses in relation to different sources of P at similar and variable application rates. Here we explore the impacts of different P sources (solely inorganic, mixed, or solely P-rich organic material), applied at three P application rates, on plant growth, nutrition and mycorrhizal responses. Tomato plants (arbuscular mycorrhizal and non-mycorrhizal plants) were grown in a soil amended with 10, 20 and 40 mg P kg⁻¹. We found that the solely inorganic P source affected mycorrhizal and non-mycorrhizal plants differently to the solely P-rich organic source, as did the combination of the two, even with P application rates matched between different sources. The solely inorganic P source consistently favoured mycorrhizal plants, whereas mycorrhizal plants performed less successfully than non-mycorrhizal plants in the solely P-rich organic source. However, mycorrhizal and non-mycorrhizal plants responded equally in the soil where the mixed P source was added. The results indicated that blending inorganic and organic P sources could be used to mitigate negative effects of AMF on plant growth and P nutrition compared to using solely P-rich organic material.