Variable temperature sensitivity of soil organic carbon in North American forests

Authors

  • CINZIA FISSORE,

    1. School of Forest Resources and Environmental Science, Michigan Technological University, 1400 Townsend Drive, Houghton, MI 49931, USA,
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    • 1Present address: Department of Soil, Water, and Climate, University of Minnesota, 439 Borlaug Hall, 1991 Upper Buford Circle, Saint Paul, MN 55108, USA.

  • CHRISTIAN P. GIARDINA,

    1. USDA Forest Service, Pacific Southwest Research Station, Institute of Pacific Islands Forestry, 60 Nowelo Drive, Hilo, HI 96720, USA,
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  • CHRISTOPHER W. SWANSTON,

    1. USDA Forest Service, Northern Research Station, 410 MacInnes Drive, Houghton, MI 49931, USA,
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  • GARY M. KING,

    1. Department of Biological Science, Louisiana State University, Baton Rouge, LA 70803, USA,
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  • RANDALL K. KOLKA

    1. USDA Forest Service, Northern Research Station, 1831 Hwy. 169 E., Grand Rapids, MN 55744, USA
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Cinzia Fissore, tel. +1 612 625 3125, fax +1 612 625 2208, e-mail: fisso001@umn.edu

Abstract

We investigated mean residence time (MRT) for soil organic carbon (SOC) sampled from paired hardwood and pine forests located along a 22 °C mean annual temperature (MAT) gradient in North America. We used acid hydrolysis fractionation, radiocarbon analyses, long-term laboratory incubations (525-d), and a three-pool model to describe the size and kinetics of the acid insoluble C (AIC), active and slow SOC fractions in soil. We found that active SOC was 2 ± 0.2% (mean ± SE) of total SOC, with an MRT of 33 ± 6 days that decreased strongly with increasing MAT. In contrast, MRT for slow SOC and AIC (70 ± 6% and 27 ± 6% of total SOC, respectively) ranged from decades to thousands of years, and neither was significantly related to MAT. The accumulation of AIC (as a percent of total SOC) was greater in hardwood than pine stands (36% and 21%, respectively) although the MRT for AIC was longer in pine stands. Based on these results, we suggest that the responsiveness of most SOC decomposition in upland forests to global warming will be less than currently modeled, but any shifts in vegetation from hardwood to pine may alter the size and MRT of SOC fractions.

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