Arbuscular mycorrhizal fungal inoculation effects on the yield and nutrition of rice under aerobic growth conditions

Micronutrients such as zinc (Zn) and iron (Fe) play a crucial role in sustaining human health. For populations around the world who depend on cereal products as their primary source of nutrition, the ability to absorb Zn and Fe in the digestive system (i.e., bioavailability) can be hindered by the presence of phytic acid, which acts as an anti-nutritional compound. Accumulation of phytic acid in grains can be affected by soil characteristics, particularly the availability of phosphorus (P), and potentially the presence of arbuscular mycorrhizal (AM) fungi. We explored how AM fungi and soil P fertilisation impact grain biomass, nutrition, phytate and the bioavailability of Zn and Fe on seven commercial rice varieties in a glasshouse-based experiment. Seven selected rice varieties including Reiziq, Langi, Sherpa, Opus, Topaz, Calrose and Nipponbare were grown with or without AM fungi (Rhizophagus irregularis) and two soil P treatments (0 or 20 mg kg-1 soil) under control room temperature on the Waite Campus from January to June 2023. The conditions were 28/22 degree centigrade day/night temperature, with 14 hour day length and 60-70% relative humidity. All seven rice varieties were well colonised with the AM fungus, with the mean root length colonised of 50%. However, the impact of AM colonisation on grain biomass and nutrition was plant variety-dependent. Generally, AM fungal colonisation generally resulted in higher grain yield under low soil P availability. However, the AM-colonised plants accumulated more P in their grain, and this led to greater phytic acid contents, and thus, lower Zn and Fe bioavailability. It is essential to develop optimal strategies for managing AM fungi, selecting rice varieties, and managing soil P inputs to not only improve on grain yield but also grain nutrient concentrations and bioavailability of Zn and Fe in rice grain.