Linking Phosphorus Sequestration to Carbon Humification in Wetland Soils by ³¹P and ¹³C NMR Spectroscopy

Abstract

Phosphorus sequestration in wetland soils is a prerequisite for long-term maintenance of water quality in downstream aquatic systems, but can be compromised if phosphorus is released following changes in nutrient status or hydrological regimen. The association of phosphorus with relatively refractory natural organic matter (e.g., humic substances) might protect soil phosphorus from such changes. Here we used hydrofluoric acid (HF) pretreatment to remove phosphorus associated with metals or anionic sorption sites, allowing us to isolate a pool of phosphorus associated with the soil organic fraction. Solution 31 P and solid state 13 C NMR spectra for wetland soils were acquired before and after hydrofluoric acid pretreatment to assess quantitatively and qualitatively the changes in phosphorus and carbon functional groups. Organic phosphorus was largely unaffected by HF treatment in soils dominated by refractory alkyl and aromatic carbon groups, indicating association of organic phosphorus with stable, humified soil organic matter. Conversely, a considerable decrease in organic phosphorus following HF pretreatment was detected in soils where O-alkyl groups represented the major fraction of the soil carbon. These correlations suggest that HF treatment can be used as a method to distinguish phosphorus fractions that are bound to the inorganic soil components from those fractions that are stabilized by incorporation into soil organic matter.

Identification of inositol hexakisphosphate binding sites in soils by selective extraction and solution 31P NMR spectroscopy

“…organic matter (Celi and Barberis, 2007). Since both the oxalic acid (García-Rodeja et al, 2007) and the HF pretreatment should have interrupted the associations between the metal bridges and organic matter (Hamdan et al, 2012) we assume that the IP 6 is either directly adsorbed to the organic matter or incorporated in it.…”

“…In comparison, the HF pretreatment procedure dissolves all minerals and therefore removes all P chelated to metals or sorbed to anionic sorption sites (Hamdan et al, 2012). Hence, pretreatment of the soils with HF should remove the amorphous as well as more crystalline minerals.…”

“…To isolate IP 6 associated with soil organic matter, soils were preextracted in 10% HF according to the procedure of Hamdan et al (2012). Briefly, soil (2.0 ± 0.01 g) was extracted four times in 45 mL of 10% HF for 1 h, and then twice for 24 h. The solution was centrifuged at 1790 g for 10 min between each step and the supernatant discarded.…”

“…Hamdan et al, 2012). Hydrofluoric acid dissolves the mineral matrix but leaves organic matter largely intact (Dougherty et al, 2007).…”

Soil organic carbon and nutrients along an alpine grassland transect across Northern Tibet

“…Previous studies have shown that the P release from rock weathering is a major factor governing the accumulation of organic matter and plays an important role in soil C turnover (Hamdan et al 2012). When P availability is limited, C turnover is inhibited because microbial biomass becomes less efficient in utilising substrates (Saggar et al 2000).…”