PARENT SESSION
Poster Session #27: Nutrient Cycling I.
Tuesday, August 6. Presentation from 5:00 PM to 6:30 PM. Exhibit Hall B & C, TCC

Patterns of nitrogen cycling at treeline and within forests along a latitudinal transect in Alaska.

LOOMIS, PATRICIA^*,1, RUESS, ROGER¹, KIELLAND, KNUT¹, ¹ University of Alaska- Fairbanks, Fairbanks, AK

ABSTRACT- Examining the rates and controls over N cycling processes between treelines and forests is useful for understanding the impact of climate warming on ecosystem N cycling. We studied soil N cycling processes across a broad range of white spruce (Picea glauca) treeline and contiguous forested sites along a latitudinal transect in Alaska. Study regions were located in the Chugach Range, the White Mountains, and the Brooks Range. We hypothesized that N cycling rates are higher in forested sites than in treeline sites, and higher in southern latitudes than northern latitudes. Nitrogen cycling was assessed using buried bags to estimate seasonal (including over winter) patterns of mineral and organic (total amino acids) N mineralization. Microbial biomass N was determined as an index of microbial sink strength. Preliminary results suggest significantly higher rates of N mineralization within pooled forest sites than at pooled treeline sites for both the growing season (late June-late July) (p<0.01) and for fall (early Aug-early Sept) (P<.05) time periods, but rates did not vary significantly for these time periods among ranges. During the growing season, rates were significantly higher in the Brooks Range for both treeline and forest sites than in the White Mountains; however, during fall, rates were significantly different only between the Brooks Range and the Chugach Range treeline sites. These results suggest that controls over N cycling rates at treeline and forests within a region differ from controls over cycling rates across regions.

KEY WORDS: treeline, nitrogen cycling