Implications for ecosystem N loss
Understanding the mechanisms controlling soil nitrification in response
to N addition and N cessation is important for accurately predicting
ecosystem potential N losses accompanying changed anthropogenic N
inputs. Results from our study showed that although elevated inorganic N
concentrations in the soil had declined to control levels after
treatments ceased, their effects on ammonia oxidizers were maintaining
high nitrification even 7 years after cessation of nutrient addition.
These results resulted from two pathways. First, soil microbial biomass
N predominantly controlled mineralization variability and soil nitrogen
availability for ammonia oxidizers after the cessation of N inputs.
Mobile N in recovering ecosystems has not the same fate as N in
unimpacted ecosystems. Second, legacy effects of the ammonia oxidizer
community due to N addition may have contributed to lasting changes in N
cycling. Together, our results indicate a high nitrification environment
induced by N enrichment is not possible simply by reducing N input, and
it requires a long recuperation time.