Phosphorus compounds in subarctic Fennoscandian soils at the mountain birch, (Betula pubescens) -: tundra ecotone

Nutrient availability will partly regulate the response of high latitude ecosystems to climate warming, but phosphorus biogeochemistry is poorly understood in Arctic soils. We used NaOH-EDTA extraction and solution P-31 nuclear magnetic resonance (NMR) spectroscopy to determine phosphorus compounds in subarctic soils from three locations in the Fennoscandian mountains contrasting in latitude and continentality. Soils were taken from open tundra and mountain birch (Betula pubescens Ehrh.) forest at each location. Between 87 and 95% of the total phosphorus was extracted from the surface 2 cm of the organic soil horizons. Most of the extracted phosphorus was orthophosphate monoesters (44-55%), with smaller concentrations of inorganic orthophosphate. (15-24%), orthophosphate diesters (12-16%), pyrophosphate (3-18%), inorganic polyphosphate (0-15%) and phosphonates (0-4%). The orthophosphate diesters were further subclassified into DNA (9-13% extracted phosphorus) and phospholipids (1-6% extracted phosphorus), although strong signals in the orthophosphate monoester region of the spectra, consistent with the degradation of phosphatidyl choline in alkaline solution, suggested that phospholipid concentrations were substantially underestimated. The phosphorus composition was broadly similar among soils from the three locations, although no phosphonates were detected in tundra soils from the most southerly site. Deeper organic horizons tended to contain a greater proportion of orthophosphate monoesters than at the surface. The abundance of phosphorus compounds that would be considered readily degradable in temperate environments probably reflects the slow organic matter decomposition in these cold, acidic soils, and suggests that phosphor-us availability is unlikely to limit ecosystem productivity on mesic soils at the birch-tundra ecotone during changes induced by climate warming. (C) 2004 Elsevier Ltd. All rights reserved.