Seasonal Variation in Nitrogen Availability and Utilization in an Acidic and Calcareous Soil

SUMMARY Pronounced seasonal trends were observed in nitrogen availability and utilization in an acidic soil supporting Deschampsia flexuosa and a calcareous soil supporting Zerna erecta. In both soils, mineralization rates and instant inorganic nitrogen concentrations were maximum in late winter/early spring after which a rapid decline occurred. A similar seasonal pattern was evident in the levels of several nitrogen‐assimilating enzymes and soluble nitrogen pools in both grasses. Fertilizer experiments indicated that in both soil types nitrate formation was limited by the ammonium supply. Despite differences in the major form of inorganic nitrogen supplied to the plants, Deschampsia and Zerna showed similar capacities to utilize ammonium and nitrate. It is suggested that the observed seasonal enzymic response in these native species may be an adaptation to the fluctuating and low nitrogen status of natural soils.