Soil nitrogen accretion along a floodplain terrace chronosequence in northwest Alaska: Influence of the nitrogen-fixing shrubShepherdia canadensis
| Autor: | Charles C. Rhoades, Robert Stottlemyer, Hlynur Oskarsson, Dan Binkley |
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| Rok vydání: | 2008 |
| Předmět: | |
| Zdroj: | Écoscience. 15:223-230 |
| ISSN: | 2376-7626 1195-6860 |
| DOI: | 10.2980/15-2-3027 |
| Popis: | Nitrogen enters terrestrial ecosystems through multiple pathways during primary succession. We measured accumulation of total soil nitrogen and changes in inorganic nitrogen (N) pools across a 300-y sequence of river terraces in northwest Alaska and assessed the contribution of the nitrogen-fixing shrub Shepherdia canadensis. Our work compared 5 stages of floodplain succession, progressing from a sparsely vegetated silt cap to dense shrubby vegetation, balsam poplar-dominated (Populus balsamifera) and white spruce-dominated (Picea glauca) mixed forests, and old-growth white spruce forest. Total soil N (0-30 cm depth) increased throughout the age sequence, initially by 2.4 g N·m -2 ·y -1 during the first 120 y of terrace development, then by 1.6 g N·m -2 ·y -1 during the subsequent 2 centuries. Labile soil N, measured by anaerobic incubation, increased most rapidly during the first 85 y of terrace formation, then remained relatively constant during further terrace development. On recently formed terraces, Shepherdia shrubs enriched soil N pools several-fold compared to soil beneath Salix spp. shrubs or intercanopy sites. Total and labile soil N accretion was proportional to Shepherdia cover during the first century of terrace development, and mineral soil δ 15 N content indicated that newly formed river terraces receive substantial N through N-fixation. About half the 600 g total N·m -2 accumulated across the river terrace chronosequence occurred during the 120 y when S. canadensis was dominant. Sediment deposited by periodic flooding continued to add N to terrace soils after the decline in Shepherdia abundance and may have contributed 25% of the total N found in the floodplain terrace soils. Keywords: floodplain forest, natural abundance N isotopes, primary succession, riparian biogeochemistry, sedimen- tation, terrestrial N cycling. |
| Databáze: | OpenAIRE |
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