Sample Pretreatment and Phosphorus Speciation in Wetland Soils

Abstract

We assessed the influence of sample pretreatment on the amounts and forms of P extracted in NaOH-EDTA (ethylenediamine tetraacetic acid) from a series of contrasting wetland soils from the Florida Everglades. Samples of unconsolidated benthic floe and underlying soil (0-10 cm) were extracted either fresh (overnight refrigeration only), air dried (10 d at ~30°C), or frozen at -80°C and lyophilized (~48 h), before extraction and solution ^'P nuclear magnetic resonance (NMR) spectroscopy. Significant differences in total P extraction following pretreatment were detected for one out of four benthic floe samples and three out of four soil samples, although the changes were inconsistent: in two cases the total P extraction increased, while in two others it decreased. Assessment of the P composition by solution ^ P NMR spectroscopy revealed differences among treatments, although these were mostly within the range of error associated with replicate analyses; however, DNA was not detected in a fresh sample of calcareous benthic floe, despite representing an important component of the organic P extracted from dried samples. The apparent sample-specific nature of the changes confirms the importance of carefully assessing pretreatment effects in studies of soil organic P in wetlands.Abbreviations: EDTA, ethylenediamine tetraacetic acid; NMR, nuclear magnetic resonance.Organic P constitutes a considerable proportion of the total P in wetland soils, so its accurate measurement is the basis for understanding P biogeochemistry in wetland ecosystems. Soil organic P is now commonly assessed by extraction in a solution containing NaOH and ethylenediamine tetraacetic acid (EDTA), with detection by solution ^'P NMR spectroscopy (Cade-Menun, 2005; Turner et ai., 2005). The single-step NaOH•EDTA extractant "was developed to quantitatively recover organic P from mineral soils (Bowman and Moir, 1993), but is particularly effective for organic soils with relatively lo"w pH, from which >90% of the total P can be extracted (e.g., Cade-Menun et al., 2000;Turner et al., 2004). It should therefore be well suited to the analysis of wetland soils and has recently been applied to a series of slightly acidic to alkaline samples from the Florida Everglades (Robinson et al., 1998;Turner et al., 2006a). Most samples analyzed so far contained a range of P compounds, including phosphate, phosphate mono-

Caution Needed in Pretreatment of Sediments for Refining Phosphorus‐31 Nuclear Magnetic Resonance Analysis: Results from a Comprehensive Assessment of Pretreatment with Ethylenediaminetetraacetic Acid

“…Triplicate extraction of a sediment sample from Lake Taihu and subsequent 31 P‐NMR analyses showed that analytical errors were generally within 10% for orthophosphate, orthophosphate monoesters, and DNA with large peaks and within 20% for phospholipids and polyphosphate with small peaks. The errors were generally consistent with the reports by Turner et al (2007) and Turner (2008) The significance of pretreatment effect on individual P compound was thus defined by >20% of the relative difference in detected concentration compared with the single‐step extraction.…”

Soil Phosphorus Forms along a Strong Nutrient Gradient in a Tropical Ombrotrophic Wetland

“…§ Superscript letters denote homogenous subsets determined by post-hoc Tu key's honestly significant difference test. Menun and Preston, 1996;Turner et al, 2007). The extraction (0.25 mol L-1 NaOH and 50 mmol L"^ EDTA) was applied to air-dried soils with shaking for 4 h, as well as fumigated and nonfumigated fresh soils after application of the AEM strips (Cheesman et al, 2010a) to assess the potential contribution of live microbial cells to the P composition of the air-dried soils.…”

Diagenesis of settling seston: identity and transformations of organic phosphorus

“…This could be explained by mineralization of diester-P and poly-P to monoester-P and ortho-P, respectively, after mineralization ceased. No final conclusion can be drawn since we only studied one pooled seston sample, but the low standard errors of the replicate seston samples (seen from the sequential fractionation and the P release experiment) combined with small standard errors involved in 31 P NMR analysis 2,34 indicate this finding to be robust. However further studies are needed to fully address this issue.…”