Optimising associations of arbuscular mycorrhizal fungi with wheat

Abstract

Arbuscular mycorrhizal fungi (AMF) are ubiquitous symbionts of most vascular plants and essential contributors to soil health for which reason their application in agriculture has been investigated extensively. In wheat as one of the staple foods where large amounts of fertiliser and pesticides are used, the integration of mycorrhizal benefits such as increased nutrient uptake and plant health is desirable, but mutualistic outcomes of the symbiosis are determined by variety, agronomic management practices as well as nitrogen (N) and phosphorus (P) content of the soil. The present study investigated the impact of different fertiliser sources (biogas digestate, farmyard manure and mineral N) on AMF at five key development stages of two wheat varieties (Aszita and Skyfall) +/- crop protection over two cropping seasons 2017-18 and 2018-19 in a P-depleted soil. Additionally, the effect of a commercial AMF inoculum (INOQ Advantage) on plant performance, yield and grain quality was assessed. AMF-root colonisation (AMF-RC) was consistently higher in the modern variety Skyfall which also showed lower abundances of native AMF in response to AMF inoculation. Biogas digestate and farmyard manure application decreased AMF-RC in both years, whereas mineral N only reduced AMFRC when soil N was high in the first season following grass-clover, but not in the second season following wheat (i.e. 2nd wheat crop). Amplicon sequencing of the ITS1-region revealed that mycorrhizal communities in roots were dominated by Glomus spp. and were not affected by agronomic management or variety. Differential abundance analyses based on sequences of the small subunit (SSU) however indicated increased diversity of fine root endopyhtes (FRE) in response to mineral N. Although the AMF inoculum was not detected in roots using strainspecific primers in digital droplet PCR, inoculation with AMF increased biomass production of wheat without fertiliser and decreased biomass production with mineral N treatment, but these changes did not affect grain yields. A pot experiment that tested a cellulose-based seed coating with the INOQ Advantage root powder showed negative effects on plant growth, but without root colonisation. The results of this study imply a key role of N that impacts AMF-RC, FRE and the effect of biostimulants. The use of such in wheat production requires further optimisation to guarantee economic benefit for farmers while excluding side-effects of exogenous strains on native AMF.