Distinct Soil Nitrogen Transformation Patterns in Adjacent Forest and Grassland Ecosystems in Central Alberta, Canada.

Land use change can alter rates of organic matter input and the quality of soil organic matter; as such distinct nitrogen (N) transformation patterns may be formed in different land use systems. The above prediction was tested by studying gross and net rates of N transformations in two adjacent land use systems (forest and grassland) in central Alberta. We found that gross N mineralization and immobilization rates were significantly higher in forest than in grassland soils, while the reverse was true for gross nitrification rates. When soils from the two land use systems were subjected to different soil moisture, temperature and acidity treatments, those soils responded to the treatments differently, again indicating that there were distinct N transformation patterns in the two land use systems. For example, increasing temperature in a laboratory incubation experiment significantly increased gross nitrification rates in the grassland soil and gross N immobilization rates in the forest soil, suggesting that grassland soils maybe more vulnerable to N loss through NO₃⁻ leaching or denitrification. Nitrous oxide emission rates corroborated the N transformation rate measurements. We conclude that the effect of land use change on N transformation in the landscape should be carefully considered with implications for the climate system and the broader environment.