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United States Department of Agriculture

Agricultural Research Service

Title: Phosphorus Composition of Upland Soils Polluted by Long-Term Atmospheric Nitrogen Deposition

Authors
item Turner, Benjamin
item Chudek, John - UNIV. OF DUNDEE, UK
item Whitton, Brian - UNIV. OF DURHAM, UK
item Baxter, Robert - UNIV. OF DURHAM, UK

Submitted to: Biogeochemistry
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: July 16, 2002
Publication Date: N/A

Interpretive Summary: Atmospheric nitrogen deposition from fossil fuel burning can enhance biological phosphorus limitation in terrestrial ecosystems and increase the importance of organic phosphorus to plants and microorganisms. This study reports the use of solutionphosphorus-31 nuclear magnetic resonance spectroscopy to determine the phosphorus composition of soils in the Upper Teesdale National Nature Reserve, northern England, an upland region influenced by such deposition for at least 150 years. Three characteristic soil types were sampled on three occasions during an annual cycle: The three characteristic soils types (blanket peat, acidic grassland soil, calcareous grassland soil) were dominated by organic phosphorus mainly in the form of recalcitrant orthophosphate monoesters, while the two acidic soils also contained large proportions of orthophosphate diesters and phosphonates, suggesting that these compounds become stabilised at low pH. A seasonal trend of increasing orthophosphate monoester-to-diester ratios, most evident in the calcareous grassland soil, indicated the preferential degradation of orthophosphate diesters during the growing season. Our results suggest that organisms able to use recalcitrant soil organic phosphorus may have a competitive advantage in environments under enhanced atmospheric nitrogen deposition.

Technical Abstract: Atmospheric N deposition can enhance biological P limitation in terrestrial ecosystems and increase the importance of organic P to plants and microorganisms. We used NaOH-EDTA extraction and phosphorus-31 NMR spectroscopy to determine the P composition of soils in the Upper Teesdale National Nature Reserve, northern England, an upland region influenced by such deposition for at least 150 years. Three characteristic soil types were sampled on three occasions during an annual cycle: blanket peat (318 mg per g total C, 607 mu per g total P, pH 3.9); acid organic soil under grassland (354 mg per g total C, 1190 mu per g total P, pH 3.7); calcareous soil under grassland (140 mg per g total C, 649 mu per g total P, pH 7.3). Between 58 and 99% of the total P in soil and litter layers was extracted by 0.25 M NaOH + 0.05 M EDTA. Extracts of all soils were dominated by organic P, mainly in the form of orthophosphate monoesters (43-69% extracted P). The two acidic soils also contained large proportions of orthophosphate diesters (6-19% extracted P) and phosphonates (7-16% extracted P), suggesting that these compounds become stabilised at low pH. However, a seasonal trend of increasing orthophosphate monoester-to-diester ratios, most evident in the calcareous grassland soil, indicated the preferential degradation of orthophosphate diesters during the growing season. Orthophosphate was the major inorganic P compound (17-34% extracted P), and all soils contained pyrophosphate (1-5% extracted P). However, orthophosphate determined in the NaOH-EDTA extracts by phosphorus-31 NMR spectroscopy was substantially greater than that determined by molybdate colourimetry, suggesting that orthophosphate occurred in complexes with humic compounds that were not detected by conventional procedures. Our results suggest that organisms able to use recalcitrant soil organic P may have a competitive advantage in environments under enhanced atmospheric N deposition.

Last Modified: 9/10/2014
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