PARENT SESSION
Oral Session # 35: Biogeochemistry III: Arctic, Alpine, and Tundra Systems.
Presiding: A Hartley
Tuesday, August 5. 1:30 PM to 5:00 PM, SITCC Meeting Room 203.
Nutrient uptake and decomposition in the forest-alpine tundra ecotone of the Colorado Front Range.
Withington, Cynthia*,1, Sanford, Robert1, 1 University of Denver, Denver, CO, USA
ABSTRACT- Nitrogen (N) and phosphorus (P) availabilities strongly influence alpine plant productivity, yet much uncertainty exists about the nutrient status of trees in the forest-alpine tundra ecotone. We hypothesize that nutrient availability decreases with elevation in this ecotone, thus contributing to stunted tree growth (krummholz) and the inability for trees to grow above treeline. Engelmann spruce (Picea engelmannii) root nutrient (N and P) contents were determined and root N and P uptake bioassays were performed for use as a comparative index of nutrient availability in surface soils at Mt. Goliath, Rogers Peak, and two transects at Niwot Ridge, Colorado. Contrary to our hypothesis, we found no significant differences in P content between krummholz (1.16 mg P g root-1 ± 0.06 SE) and closed forest (1.16 mg P g root-1 ± 0.09 SE) roots. Similarly, there were no significant differences in P uptake between krummholz (0.483 mg P g root-1 15 min.-1 ± 0.091 SE) and closed forest (0.471 mg P g root-1 15 min.-1 ± 0.063 SE) roots. These results are surprising because previous studies of Engelmann spruce needles have shown less phosphorus in krummholz than upright trees. Nitrogen content in spruce roots and N uptake results are compared as well. Because nutrient availability is believed to vary with organic turnover and decomposition, these results are interpreted in the context of a year-long decomposition study with N and P treatment effects using an experimental design in the field with cotton strip assays.
Key words: decomposition, phosphorus, treeline, nitrogen