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Faculty for Biology, Chemistry and Earth Sciences

Department Soil Ecology - Prof. Dr. Eva Lehndorff

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Berg, B; Dise, N: Validating a new model for N sequestration in forest soil organic matter, Water, Air and Soil Pollution: Focus, 4, 343-358 (2004), doi:10.1023/B:WAFO.0000028364.20052.a3
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 (Nlimit), giving the N concentration in the hypothesized stable remains. The Nlimit 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
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