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Abstract



Citation. Zak, D. R.; Grigal, D. F. 1991. Nitrogen mineralization, nitrification and denitrification in upland and wetland ecosystems. Oecologia 88:189-196.   [1218  LTER]

Summary. Nitrogen mineralization, nitrification, denitrification, and microbial biomass were evaluated in four representative ecosystems in east-central Minnesota. The study ecosystems included: old field, swamp forest, savanna, and upland pin oak forest. Due to a high regional water table and permeable soils, the upland and wetland ecosystems were separated by relatively short distances (2 to 5 m). Two randomly selected sites within each ecosystem were sampled for an entire growing season Soil samples were collected at 5-week intervals to determine rates of N cycling processes and changes in microbial biomass. Mean daily N mineralization rates during five-week in situ soil incubations were significantly different among sampling dates and ecosystems. The highest annual rates were measured in the upland pin oak ecosystem (8.6 g N m-2 yr-1), and the lowest rates in the swamp forest (1.5 g N m-2 yr-l); nitrification followed an identical pattern. Denitrification was relatively high ill the swamp forest during early spring (8040 micrograms N2O-N m-2 d-1) and late autumn (2525 micrograms N2O-N m-2 d-1); nitrification occurred at rates sufficient to sustain these losses. In the well-drained uplands, rates of denitrification were generally lower and equivalent to rates of atmospheric N inputs. Microbial C and N were consistently higher in the swamp forest than in the other ecosystems; both were positively correlated with average daily rates of N mineralization. In the subtle landscape of east-central Minnesota, rates of N cycling can differ by an order of magnitude across relatively short distances.

Keywords. N mineralization, Nitrification, Microbial biomass, Denitrification, Spatial variability


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