Manganese oxide affects nitrification and ammonia oxidizers in subtropical and temperate acid forest soils

Variations in nitrification dynamics were observed both in temperate and subtropical acidic forest soils. The effect of Mn on nitrification was studied to explain variation in nitrification between different soil types. Weakly and highly acidic soils in subtropical and temperate forests were treated with 0% or 3% birnessite. The nitrification process was simulated by kinetic model. Dynamic changes of amoA gene abundance of ammonia monooxygenase (AMO) for ammonia-oxidizing bacteria (AOB) and ammonia-oxidizing archaea (AOA) were estimated by qPCR. Nitrification rates were significantly decreased by Mn addition in 3 days both for the weakly acidic subtropical and temperate soils. However, the total nitrification rate did not change for either soil by Mn addition after 10 days' incubation. Nitrification was best fitted by a first-order kinetic model for both weakly acidic soils. However, it was best fitted with a zero-order model after MnO2 addition. Numbers of AMO amoA gene copy decreased after Mn addition. No significant nitrification was observed for highly acidic soils and Mn had a minimal effect. Soil nitrification was retarded by 3% MnO2 for both subtropical soil and temperate soils. Nitrification dynamics were altered by MnO2 in weakly acidic soils, probably due to Mn toxicity.