LONG-TERM RESPONSES TO FACTORIAL, NPK FERTILIZER TREATMENT BY ALASKAN WET AND MOIST TUNDRA SEDGE SPECIES

At thirteen sites in northern and central Alaska, full factorial and partial factorial NPK fertilizer experiments were completed in wet and moist tundras. The effects of the fertilizers on N and P concentrations in leaves, leaf mass per tiller, tillering, and flowering of the dominant sedge species (Eriophorum vaginatum, E, angustifolium, and Carex aquatilis) were documented for 3-10 yr at each site. Almost all sites showed at least some response to the fertilizer treatment, but the specific treatments and elements that caused the responses varied greatly among sites. There also was no consistent difference in responses between wet and moist sites. There was, however, a consistent temporal pattern to the responses observed, starting with increases in N and P concentration in leaves in the year that fertilizer was added, followed by growth and tillering responses in the second year, and increased flowering in the third year. The increases in N concentration generally only appeared in the first year, while increased P concentrations were sustained for 3-4 yr. Effects of fertilizer on flowering were still significant after 6 years in some cases. Results are discussed in terms of the role of ''nutrient limitation'' in structuring arctic plant communities and determining their productivity following disturbance or fertilization.