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Soil Warming and Carbon Loss from a Lake States Spodosol

Dep. of Biology, Grand Valley State Univ., Allendale, MI 49401-9403

Diana L. Randlett and Donald R. Zak

School of Natural Resources and Environment, Univ. of Michigan, Ann Arbor, MI 48109-1115

*Corresponding author (macdonan{at}gvsu.edu).

ABSTRACT

Elevated soil temperatures may increase C loss from soils by accelerating microbial respiration and dissolved organic C leaching. We evaluated the effect of elevated soil temperatures on C losses from a forest Spodosol by incubating soil cores from surface (Oa + A + E) and subsurface (Bhs) horizons at two seasonal temperature regimes. One regime simulated the normal course of soil temperatures in northern lower Michigan, and the other simulated soil temperatures representing an amount of warming that might occur under some global warming theory calculations. We measured the amounts of CO₂-C respired and dissolved organic C leached from the soil cores during a 33-wk period. Microbial respiration rates, after adjustment for variation in initial rates, were significantly increased by soil warming and were greater in surface than in subsurface horizons. Warming significantly increased cumulative C respired, with greater losses from surface soils (50 mg C g^-1 C) as compared with subsurface soils (25 mg C g^-1 C). Mean quantities of dissolved organic C leached, ranging from 2.3 to 3.2 mg C g^-1 C, did not differ significantly by soil horizon or temperature regime. Increased microbial respiration in surface soil horizons was the process most responsive to soil warming in the Spodosol samples we examined. Whether this is a short-term effect that would disappear once pools of labile C are exhausted, or represents a long-term response to soil warming, remains uncertain.

Received for publication July 15, 1996.