Urea hydrolysis and nitrification in arctic salt-marsh soils: Possible constraints on the growth of forage plants
1999
Wilson, Deborah J. | Wal, René van der | Chang, Esther R. | Jensen, Arne | Jefferies, Robert L.
Lesser snow geese graze intensively on graminoid vegetation of intertidal and non-tidal salt marshes at La Pérouse Bay, Manitoba. The replacement of defoliated plant tissue is limited by the supply of nitrogen. Nitrogen in goose faeces may become available for plant uptake through hydrolysis of urea and through nitrification. In recent years, heavy grazing and grubbing by the growing goose population have damaged the vegetation at some sites. Soils beneath damaged swards become hypersaline and grubbed soils exhibit low rates of net nitrogen mineralization and low ammonium concentrations. We measured effects of temperature and salinity on the rate of urea hydrolysis and on the nitrification potential of soils. Rates of urea hydrolysis increased with rising temperatures (1°C - 30°C) but declined with increasing salinity. Rates of urea hydrolysis were low in soils where the vegetation had been removed by grubbing but high in the more organic soils of the non-tidal inland marsh. Rates of nitrification were consistently low, particularly in soils from the inland marsh. The nitrification rate increased with temperature, and was higher at the salinity of sea water than at lower or higher salinities. Watering turves with river water for six weeks before measuring rates of nitrification did not significantly change the results in soils from either the intertidal marsh or the inland marsh. It is probable that most mineral nitrogen available to plants growing in these soils is in the form of ammonium. Low soil temperatures and hypersaline conditions limit rates of urea hydrolysis, and likely restrict available nitrogen for the growth of forage plants.
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