IngentaConnect Validating a New Model for N Sequestration in Forest Soil Organic...

Abstract:

A conceptual model for N sequestration into the terrestrial nitrogen (N) sink is presented. The model uses foliar litter-fall data, limit values for litter decomposition, and calculated N concentration at the limit value (N_limit), giving the N concentration in the hypothesized stable remains. The N_limit values were determined extrapolating a linear relationship between accumulated litter mass loss and the increasing litter N concentration to the limit value. The sequestration rates for N in boreal forest humus were calculated and validated for a Scots pine (Pinus sylvestris L.) monocultural stand and mixed stands with Scots pine, Norway spruce (Picea abies L.), and silver birch (Betula pendula L.). The calculated stable N fraction was compared to actually measured amounts of N in humus layers that started to accumulate 2984, 2081, 1106, and 120 yr BP. Sequestration rates of N were measured to be 0.255, 0.221, 0.147, and 0.168 g m^-2 yr^-1 and modeled to be 0.204, 0.207, 0.190, and 0.190 g m^-2 yr^-1, respectively, with missing fractions being 11.0, 1.5, 30.8, and 13.3%, respectively. The more N-rich the litter, the larger was the N fraction sequestered. This was found for experimental Scots pine needle litter (n = 6) and for 53 decomposition studies, encompassing seven litter species. The amounts of N sequestered annually ranged from ca. 1–2 kg ha^-1 yr^-1 under nutrient-poor boreal conditions to about 30 kg ha^-1 yr^-1 in temperate, more nutrient-rich forests.

Keywords: C sequestration; C sink; humus; model; N sequestration; N sink; soil organic matter

Document Type: Research article

DOI: 10.1023/B:WAFO.0000028364.20052.a3

Affiliations: 1: Lehrstuhl für Bodenökologie, BITÖK, Postfach 101251, Universität Bayreuth, Dr-Hans-Frisch-Strasse 1-3, DE-954 48, Bayreuth, Germany (author for correspondence, bjoern.berg@bitoek.uni-bayreuth.de, phone: +49 (171) 858 8212, Fax: +49 (921) 555799), Email: bjoern.berg@bitoek.uni-bayreuth.de 2: Department of Earth Sciences, The Open University, Milton Keynes, MK7 6AA, U.K. Present address: Department of Biology, Villanova University, Villanova, Pennsylvania 19085, U.S.A.

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Validating a New Model for N Sequestration in Forest Soil Organic Matter