PARENT SESSION
Oral Session #52: Carbon and Nitrogen Cycling: Soil processes and patterns. Presiding: F. Gilliam.
Wednesday, August 8, 2001. 1:00 PM to 5:00 PM. Hall of Ideas E.
Soil carbon and nitrogen dynamics on tundra landscapes with different glacial histories.
HOBBIE, SARAH1, MILEY, TIFFANY1, WEISS, MARISSA2, 1 2
ABSTRACT- We compared carbon and nitrogen (N) cycling in soils of two adjacent sites in the foothills region of the Brooks Range, Alaska, that were glaciated 10,000 and 60,000 years ago, respectively. The young site has higher soil pH and base cation availability and a plant community dominated by herbaceous species (sedges and forbs), non-Sphagnum mosses, and some deciduous shrubs. The older acidic site is dominated by deciduous and evergreen shrubs, including the woody shrub Betula nana, and Sphagnum mosses. We expected soil organic matter decomposition and N cycling to be faster at the younger site, because of higher soil pH and higher quality organic matter inputs. In contrast to our expectations, field and laboratory rates of soil respiration were lower at the young site compared to the old site, even though addition of lime strongly stimulated soil respiration at the older site. Soils from both sites immobilized N during short-term (28-day) incubations, and immobilization was greater in soils from the younger site. Adding lime caused soils from the older site to switch from immobilization to net mineralization. Cumulative inorganic N leached from soils over a period of 225 days also responded strongly to lime addition at the older site. In summary, despite short-term limitation of organic matter cycling by low pH at the older site, organic matter cycling is generally slower at the younger less acidic site.
KEY WORDS: carbon, nitrogen, tundra, Alaska