Spatial and Temporal Variability of Nitrogen Cycling in Northern Lower Michigan

Washington D.C.

1990

S. 367-380

3 Abb., 3 Tab., 31 Lit. Ang.

Bandaufführung

7380

64569

Net N mineralization and nitrification were studied in three forest ecosystem to gain an understanding of the spatial and temporal variability of N transformations. The upland forests studied were two sugar maple ecosystems that differed in overstory associates and ground flora composition, and an oak ecosystem. Three stands in each ecosystem were sampled to provide spatial replication within a 250,000 ha area in northwestern Lower Michigan. Overstory biomass and annual increment were estimated using species-specific allometric biomass equations. Net N mineralization and nitrification were determined by an in situ buried polyethylene bag technique in which surface soil samples were incubated at monthly intervals for one year. Litter was collected during autumn in each ecosystem from one randomly selected stand. Aboveground biomass was lowest in the oak ecosystem (151 t ha-1) and greatest in the sugar maple- baswood/Osmorhiza ecosystem (209 t ha-1). Net annual N mineralization was 313 ug N g-1 yr-1 in the oak ecosystem and was significantly less than annual mineralization in the two sugar maple ecosystems. Mineral N production in the sugar maple-basswood/Osmorhiza and sugar maple-red oak/Maianthemum ecosystems was 426 and 382 ug N g-1 yr-1, respectively. Nitrification was greatest in the sugar maple-basswood/Osmorhiza ecosystem where 85% of mineral N was oxidized to NO3- (364 ug ng-1 yr-1). Results suggest that ecosystem types may be used to predict spatial patterns of N transformations at regional scales.