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.
Organic matter accumulation and turnover in Dry Valley soils of Antarctica.
Barrett, John1, Virginia, Ross1, Parsons, Andy2, Porazinska, Dorota2, Wall, Diana2, 1 2
ABSTRACT- The Antarctic Dry Valleys are among the most extreme soil environments on earth, yet microbial and invertebrate abundances are comparable to hot deserts. Due to the lack of vascular plants in the Dry Valleys, sources of organic matter were historically thought to be largely from allochthonous inputs of carbon (C). Recently, Burkins et al. (2000) have shown that Taylor Valley soil organic matter bears isotopic compositions indicating mixed sources but including a large proportion of organic matter from in situ production. We used gas exchange, incubation and isotopic techniques to estimate C turnover and to distinguish in situ from allochthonous sources of organic matter. Laboratory incubations indicate that 10-20 % of the organic C is readily available to soil microbes, and in situ soil respiration measurements suggest that this pool may turn over relatively rapidly (30 yr). Isotopic composition of particulate fractions show that multiple sources of organic matter are available to support Dry Valley food webs. We conclude that low rates of potential production estimated in laboratory incubations are adequate to support observed rates of soil respiration while legacy organic matter may be relatively un-utilized by consumers. We propose a soil organic matter model composed of two pools; an active pool that turns over at decadal time scales and legacy organic matter associated with a fine particulate fraction that may cycle over centuries to millennia.
KEY WORDS: soil organic matter, soil respiration , extreme environments, Antarctic Dry Valleys