Arbuscular Mycorrhizal (AM) fungi form mutualistic symbiotic relationships with approximately 80% of terrestrial plant species, while producing the glycoprotein glomalin as a structural support molecule along their mycelial network. Glomalin confers two benefits for soils: (1) acting as a carbon and nitrogen storage molecule; (2) the binding of soil microaggregates (<250 µm) to form larger, more stable structures. The present study aimed to test the hypothesis that a correlation between glomalin and soil aggregation exists and that this is influenced by the method of seedbed preparation. The soils from two crops of winter wheat in Hertfordshire, UK, practising either conventional (20 cm soil inversion) or zero tillage exclusively, were sampled in a 50 m grid arrangement over a 12 month period. Glomalin and water stable aggregates (WSA) were quantified for each soil sample and found to be significantly greater in zero tillage soils compared to those of conventional tillage. A stronger correlation between WSA and glomalin was observed in zero tillage (Pearson’s coeffect 0.85) throughout the cropping year compared to conventional tillage (Pearson’s coeffect 0.07). The present study was able to conclude that zero tillage systems are beneficial for AM fungi, the enhancement of soil glomalin and soil erosion mitigation.

Zero till cropping systems typically apply broad-spectrum herbicides such as glyphosate as an alternative weed control strategy to the physical inversion of the soil provided by cultivation. Glyphosate targets 5-enolpyruvylshikimate-3-phosphate (EPSP) synthase in plants. There is growing evidence that this may have a detrimental impact on non-target organisms such as those present in the soil microbiome. Species of commercial importance, such as arbuscular mycorrhizal (AM) fungi that form a symbiotic relationship with plant roots are an important example. This study investigates the impact of soil cultivation and glyphosate application associated with conventional tillage (CT) and zero tillage (ZT) respectively on AM fungi populations under field and glasshouse conditions. Topsoil (<10 cm) was extracted from CT and ZT fields cropped with winter wheat, plus non-cropped control plots within the same field boundary, throughout the cropping year. Glyphosate was applied in glasshouse experiments at rates between 0 and 350 g L⁻¹. Ergosterol, an indicator of fungal biomass, was measured using high performance liquid chromatography before and after glyphosate application. Fungal root arbuscules, an indicator of AM fungi–root symbiosis, were quantified from the roots of wheat plants. Under glasshouse conditions root arbuscules were consistently higher in wheat grown in ZT field extracted soils (P = 0.01) compared to CT. Glyphosate application however inhibited fungal biomass in both the ZT (P < 0.00001) and CT (P < 0.001) treatments. In the absence of glyphosate, the number of stained root arbuscules increased significantly. Ergosterol levels, used as a proxy for fungal biomass, remained lower in the soil post glyphosate application. The results suggest that CT has a greater negative impact on AM fungal growth than ZT and glyphosate, but that glyphosate is also detrimental to AM fungal growth and hinders subsequent population recovery.

Arbuscular mycorrhizal (AM) fungi are one of the most common fungal organisms to exist in symbiosis with terrestrial plants, facilitating the growth and maintenance of arable crops. Wheat has been studied extensively for AM fungal symbiosis using the carcinogen trypan blue as the identifying stain for fungal components, namely arbuscles, vesicles and hyphal structures. The present study uses Sheaffer blue ink with a lower risk as an alternative to this carcinogenic stain. Justification for this is determined by stained wheat root sections (n=120), with statistically significant increases in the observed abundance of intracellular root cortical fungal structures stained with Sheaffer blue ink compared to trypan blue for both Zulu (P=0.003) and Siskin (P=0.0003) varieties of winter wheat. This new alternative combines an improved quantification of intracellular fungal components with a lower hazard risk at a lower cost.