Arbuscular mycorrhizal fungi drive soil nitrogen transformation under wheat varieties with different nitrogen utilization efficiencies

Arbuscular mycorrhizal fungi (AMF) can play important roles in plant nitrogen (N) uptake and use. However, it is still not well explored how AMF interact with host plants representing different N use types and thereby affect soil N transformation. A pot experiment was conducted to test the effects of AMF on N mineralization, nitrification, denitrification and nitrous oxide (N₂O) reduction in soils under wheat varieties with high and low pre-anthesis N utilization efficiency (also called grain-specific N efficiency). Our results showed that AMF can increase N mineralization potential, with a greater effect for varieties with high N utilization efficiency. AMF also increased nitrification potential, ammonium oxidation potential, but did not nitrite oxidation potential, suggesting that AMF only act on the first nitrification step (ammonium oxidation). AMF increased NO₃ ⁻ but decreased NH₄ ⁺ concentrations irrespective of the N use type of host plant. Moreover, AMF significantly increased denitrifying enzyme activity of the varieties with low N utilization efficiency, but decreased it for the varieties with high N utilization efficiency. N₂O emission during soil incubation was in tandem with denitrification. Finally, AMF significantly increased N₂O reductase activity irrespective of the N utilization efficiency of the host plant. The findings suggest that an interaction between the N utilization efficiency of wheat plants and AMF can modulate the N uptake of the host plant, and also regulate soil N transformation; a mechanism which may greatly affect the sustainability of wheat cropping systems.