SOIL AERATION IN RELATION TO SOIL PHYSICAL-PROPERTIES, NITROGEN AVAILABILITY, AND ROOT CHARACTERISTICS WITHIN AN ARCTIC WATERSHED

The seasonal change in soil oxygen availability was determined in seve ral habitats along a topographic moisture gradient in an arctic waters hed. The effect of changes in soil aeration on soil chemical and plant properties was examined by comparison of the driest (tussocks) and we ttest (wet sedge tundra) sites along this gradient. Spatial variabilit y and seasonal change in soil oxygen availability was closely linked t o the hydrologic regime and the thickness of the organic soil horizon. The greatest extension of the aerobic soil layer was found beneath we ll-drained tussocks, while less than 10% of the unfrozen soil layer is aerated in flooded wet sedge tundra. Intertussock areas and watertrac ks (channels of water drainage) have intermediate levels of aeration. In tussock tundra, soil oxygen diffusion is restricted in the mineral soil layer below the organic horizon due to reduced pore space. Organi c matter constituents and their change with depth were similar beneath tussocks and in wet sedge tundra, indicating that factors other than soil aeration (e.g. low soil temperatures, short growing season) are t he primary controls on decomposition in these two arctic tundra system s. NH4+, the dominant form of inorganic N, was more available in wet s edge tundra than in tussock tundra. At both sites, extractable and soi l solution NO3- concentrations increased 4 to 8 fold in the second par t of the growing season, indicating increased nitrifier activity with improved soil oxygen availability. Although soils thawed as deep as 60 cm, approx. 90% of the root biomass was concentrated within 20 cm of the surface. Despite the anaerobic soil environment in wet sedge tundr a, the dominant species there, Eriophorum angustifolium, reached sligh tly greater rooting depths than E. vaginatum, whose roots grow in the elevated, aerobic portion of tussocks. E. angustifolium had a root por osity of 31%, within the range found for wetland species, while roots of E. vaginatum had a porosity close to 12%. Rhizome porosity were low in both species (11%).