Poster Session # 13: Biogeochemistry, Photosynthesis, and Respiration.

Tuesday, August 5 Presentation from 5:00 PM to 6:30 PM. SITCC Exhibit Hall B.

Above- and belowground contributions to nitrogen cycling in aspen forest and northern prairie.

Steinaker, Diego*,1, Wilson, Scott1, 1 University of Regina, Canada, Regina, Saskatchewan, Canada

ABSTRACT- Studies of nitrogen dynamics typically focus on aboveground production, and report greater N inputs to the soil from primary production (NPP) in forest than in prairie. But belowground NPP is often greater than aboveground, and the true values of N input from primary production, therefore, may be different than previously appreciated. Our main goal was to quantify the contributions of above- and belowground biomass to nitrogen cycling in adjacent aspen (Populus tremuloides) forest and mixed-grass prairie habitats, at the northern edge of Great Plains, in Saskatchewan, Canada. Aboveground NPP and N input to the soil (N input = NPP x [N]) was determined from herbaceous plants litter production in both habitats. Belowground NPP and N input was measured using a combination of observation using minirhizotron images and destructive sampling. NPP and N inputs from aboveground biomass were three times greater in forest than prairie, but productivity and N inputs from aboveground were small compared with those from belowground. Root production accounted for about 75 % and 90 % of total primary productivity in forest and prairie respectively. Root length and mass was greater in forest than in prairie, but length and mass production did not differ significantly between the habitats. Although nitrogen concentration was higher in forest than in prairie roots, annual N input to the soil from fine roots was not significantly different between habitats. Our results show that biomass production and nitrogen inputs via fine roots greatly exceeded those from foliar litter. As a result, N input from total primary productivity in prairie was at least comparable to forest.

Key words: Fine roots, Nitrogen cycling, Minirhizotron, Populus tremuloides