Arbuscular Mycorrhizal Fungi Can Improve the Water Use and Phosphorus Acquisition Efficiencies of Aerobically Grown Rice

Abstract

Most rice production is conducted in flooded (anaerobic) soil conditions, but aerobic rice cultivation presents several potential benefits: increased grain water use efficiency (gWUE), reduced methane emissions, and minimised loss of phosphorus (P). Arbuscular mycorrhizal (AM) fungi are more effective at colonising and functioning in rice under aerobic soil conditions, and this rice-AM fungi association could increase both gWUE and P acquisition efficiency (PAE). We used a precision irrigation platform to apply watering treatments (60% or 80% of soil field capacity) throughout the experiment. Four commercial Australian rice varieties were grown with or without inoculation with Rhizophagus irregularis, and with addition of P fertiliser at 10 or 25 mg P kg^–1 soil. Plants were grown to maturity (134–188 days after planting), after which grain yield, plant water use, gWUE, and PAE were determined. Overall, R. irregularis inoculation increased gWUE in all four rice varieties (by a mean of 14.4%), and increased grain yield and PAE in two varieties. Grain yields were primarily constrained by low water availability (mean 48.4% reduction), but P availability also limited yield in two varieties. Of the four, Topaz showed the greatest response to AM fungal inoculation, with increased qWUE and PAE. There is potential for AM fungal inoculation to increase the water use and P acquisition efficiencies of aerobically grown rice. However, the extent of these benefits depends on the specific rice variety, which highlights the importance of variety selection in transitioning to aerobic rice production in temperate regions and in enhancing the resilience of rice cultivation to climate change.