Influence of biological nitrification inhibition by forest tree species on soil denitrifiers and N2O emissions

Abstract Some forest tree species are able to carry out a process known as biological nitrification inhibition, BNI, i.e. they inhibit nitrifiers through the production of specific compounds. We tested the hypothesis that, by restricting N supply to NO2−- and N2O-reducers, BNI would decrease potential N2O production and consumption and in situ N2O emissions. as compared to soils under trees without BNI capacity. Soils were collected from long-term monocultures (>43 ys) of three tree species without BNI capacity (Fagus sylvatica, Pinus nigra and Pseudotsuga menziesii) and two tree species with BNI capacity (Abies nordmanniana and Picea abies). The level of limitation of denitrification by NO3− was high for species with BNI capacity and low for species without BNI capacity, and was correlated with potential nitrification rates and the abundances of genes specifically harboured by ammonia oxidizing archaea and Nitrobacter. However, potential denitrification and actual N2O emissions did not reflect the tree BNI status, and denitrification limitation by soil carbon was higher than limitation by N under three tree species. Structural equation modelling revealed that the ratio between the gene copy abundances of nitrite-reducers and N2O-reducers was the microbial variable that best explained N2O emissions, along with soil pH and moisture. In addition, the NO3− concentration in the soil solution at 60 cm depth increased with the potential nitrification-to-denitrification ratio, suggesting a higher risk of NO3− leaching under some tree species like Douglas fir.