Abstract
Microorganisms play an important role in the acquisition and transfer of nutrients in soil and plants. They are involved in a range of processes that affect nutrient transformations and thus influence the subsequent availability to plant roots. But nutrient availability will also influence microbial diversity and function. Multispecies microbial inoculants may have dual functions as biostimulants and biocontrol agents and claimed agricultural benefits are influential for regulatory purposes. Biostimulants include commercial products containing substances or microorganisms that stimulate plant growth and can be involved in a range of processes that affect nutrient transformations in soil and thus influence nutrient availability, and types of fertilisers can influence soil microbial diversity and function. A glasshouse experiment was conducted at The University of Western Australia using wheat (cv. Wyalkatchem) to investigate the effects of different forms of mineral and chemical fertilisers along with application of a multispecies microbial inoculant. The experimental design was a randomised complete block with three replications of two distinct Australian Mineral Fertilisers (AMF1 and AMF2), and a chemical fertiliser with and without a microbial inoculant combination. The treatments were: control, mineral fertiliser (AMF1) without microbes, mineral fertiliser (AMF1) with microbes, mineral fertiliser (AMF2) without microbes, mineral fertiliser (AMF2) with microbes, chemical fertiliser (CF) without microbes, and chemical fertiliser (CF) with microbes. Despite an early reduction in plant shoot growth with chemical fertiliser + inoculant microbes, the microbial inoculant + mineral fertiliser treatments increased shoot growth compared to the control. At maturity, application of all fertilisers with or without the multispecies microbial inoculant increased grain yield compared to control. The fertiliser and inoculation of microbes influenced mycorrhizal root colonisation. Using 16S rRNA sequencing, the microbial inoculant and fertiliser treatments were shown to influence the diversity of rhizosphere bacteria. Overall, the multispecies microbial inoculant had beneficial effects on wheat yield when they were combined with the mineral and chemical fertilisers applied at the level recommended for on-farm use in south-western Australia.