Arable agriculture urgently requires sustainable solutions to reduce reliance on large inputs of nutrient fertilisers to continue to improve crop yields. By harnessing the symbiosis between arbuscular mycorrhizal fungi (AMF) and plants, there is potential to enhance plant nutrient assimilation and growth with fewer additional inputs, such as chemical-based fertilisers. However, the efficacy of commercially-available mycorrhizal inocula in agricultural systems remains controversial. There is a pressing need to assess the functional significance of AMF inocula in crops across cultivars to successfully exploit AMF in agriculture. Moreover, climate change is now negatively impacting agricultural productivity, and we know little about how increasing atmospheric [CO2] will change the functionality of mycorrhiza-crop relationships.
Using isotope tracers ( 14C, 33P and 15N), I measured carbon-for-nutrient exchange between wheat and AMF symbionts with- and without the addition of a commercially available active mycorrhizal inoculum (Rhizophagus irregularis) to a non-sterile agricultural soil to simulate in-field application scenarios. I quantified whether the response to R. irregularis inoculum was cultivar-specific using three elite wheat cultivars in common use in rotations today. Inoculation with AMF increased phosphorus uptake across all wheat cultivars, although the increase was not directly attributable to mycorrhizal fungi and there were significant cultivar differences in carbon-for-nutrient exchange stoichiometry.
Using T-RFLP to analyse the community composition in wheat roots, I found R. irregularis introduced via inoculation established in the soil and successfully colonised all cultivars. This suggests there is an increased likelihood that any responses of the wheat cultivars to inoculation were directly due to R. irregularis colonisation and associated rhizobacteria rather than any facilitation effects on the native AMF community.
AMF functioning can be highly context dependent and strongly driven by environmental factors. Therefore, due to the increasing interest in the application of commercially available AMF inoculants in agricultural soils, it was important to quantify changes in carbon-for-nutrient exchange between the cultivars and R. irregularis at elevated atmospheric [CO2] (in line with IPCC projections for atmospheric CO2 concentrations in 2100). I found no evidence for enhanced carbon-for-nutrient exchange at elevated [CO2], addressing a critical knowledge gap of how fungal inoculants, which could function well in current systems, will respond to future climates.
