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Soil Nitrogen, Microbial Biomass, and Respiration along an Arctic Toposequence

Biological Sciences Center, Desert Research Inst., P.O. Box 60220, Reno, NV 89506

R. A. Virginia

Environmental Studies Program, Dartmouth College, Hanover, NH 03755

S. F. Oberbauer

Dep. of Biological Sciences, Florida Univ., Miami, FL 33199

C. T. Gillespie

730 CES/CEVN, 1172 Iceland Ave., Vandenberg Air Force Base, CA 93437-6011

J. F. Reynolds

Dep. of Botany, Duke Univ., Durham, NC 27708

J. D. Tenhunen

Bayreuther Institut für Ökosystemforschung, Universität Bayreuth, W-8580 Bayreuth, Germany

*Corresponding author (wcheng{at}dri.edu).

ABSTRACT

To investigate the interactions among mineral N, C availability, microbial biomass, and respiration in arctic soils, we sampled soils five times during a growing season from a toposequence on a slope in northern Alaska. The toposequence consisted of six vegetative types from the ridge top to the stream bank: lichen heath, dry cassiope, moist carex (Carex spp.), water track, tussock tundra (intertussock), and riparian. The spatial distribution and temporal variation of soil mineral N, microbial biomass, soil C availability, and C turnover were soil type dependent. During the growing season, the concentration of soil NH⁺₄-N decreased in tussock tundra soils but increased in lichen heath soils. Soil C availability at all locations was the highest at the beginning of the growing season and declined thereafter. The C availability index (CAI) and the potential C turnover rate increased as soils became wetter. Tussock-forming tundra soil was generally colder than other sites and had high C/N ratios, low amounts of mineral N, and a low potential C turnover index, and therefore, was the least biologically active type. In contrast, water track was the most biologically active site in the sequence and had the highest C and N availability, the highest potential C turnover index, and the highest microbial biomass C and N. The mosaic of diverse plant communities and soil types that comprise arctic landscapes necessitates that accurate estimates of large-scale C or N budget can only be made by integration of all types of plant communities and soils.

Received for publication October 4, 1996.