Abstract Description

Arbuscular mycorrhizal (AM) fungi provide important agricultural services through forming symbiotic associations with crops. The success of this interaction can be negatively impacted by some soil management practices, such as the inclusion of non-hosts of AM fungi in crop rotations. We used high-throughput sequencing to characterise the AM fungal communities in the rhizosphere of wheat (mycorrhizal), medic (mycorrhizal), canola (non-mycorrhizal) or wheat at two farms. This was coupled with analysis of mycorrhizal root colonization and spore densities. Relationships between AM fungal communities and abundance with soil parameters were also examined. Pre-cropping with canola did not negatively impact AM fungal diversity in the soils of the subsequent wheat crop. Notably, species richness tended to be higher in the canola-wheat soils, although statistically insignificant. Soil properties significantly influenced AM fungal communities, particularly species richness, which was negatively correlated with available phosphate (P) and positively correlated with available nitrogen (N), potassium and calcium. Similarly, wheat root colonization increased in response to a decrease in soil P with a concomitant increase in N, from 21 % to 55.8 % at one of the farms, highlighting the importance of the soil N/P ratio on AM fungal root colonization. On the contrary, spore densities increased in response to increasing soil P levels, suggesting that sporulation may be an AM fungal strategy for surviving adverse conditions. AM fungal genera, namely, Rhizophagus, Dominikia and Glomus OTU richness were shown to respond differently to soil nutrients, highlighting differences in sensitivity to soil nutrients by AM fungal species. Our findings suggest that in the short term, the inclusion of canola in wheat rotations does not necessarily translate to a decline in AM fungal diversity and abundance. It is also possible that canola may be a rudimentary host of AM fungi. Soil physicochemical properties on the other hand, should be managed to ensure high diversity and abundance of AM fungi in agricultural soils.