The stable oxygen isotope ratio of resin extractable phosphate derived from fresh cattle faeces

Abstract

RationalePhosphorus losses from agriculture pose an environmental threat to watercourses. A new approach using the stable oxygen isotope ratio of oxygen in phosphate (δ18OPO4 value) may help elucidate some phosphorus sources and cycling. Accurately determined and isotopically distinct source values are essential for this process. The δ18OPO4 values of animal wastes have, up to now, received little attention.MethodsPhosphate (PO4) was extracted from cattle faeces using anion resins and the contribution of microbial PO4 was assessed. The δ18OPO4 value of the extracted PO4 was measured by precipitating silver phosphate and subsequent analysis on a thermal conversion elemental analyser at 1400°C, with the resultant carbon monoxide being mixed with a helium carrier gas passed through a gas chromatography (GC) column into a mass spectrometer. Faecal water oxygen isotope ratios (δ18OH2O values) were determined on a dual‐inlet mass spectrometer through a process of headspace carbon dioxide equilibration with water samples.ResultsMicrobiological results indicated that much of the extracted PO4 was not derived directly from the gut fauna lysed during the extraction of PO4 from the faeces. Assuming that the faecal δ18OH2O values represented cattle body water, the predicted pyrophosphatase equilibrium δ18OPO4 (Eδ18OPO4) values ranged between +17.9 and +19.9‰, while using groundwater δ18OH2O values gave a range of +13.1 to +14.0‰. The faecal δ18OPO4 values ranged between +13.2 and +15.3‰.ConclusionsThe fresh faecal δ18OPO4 values were equivalent to those reported elsewhere for agricultural animal slurry. However, they were different from the Eδ18OPO4 value calculated from the faecal δ18OH2O value. Our results indicate that slurry PO4 is, in the main, derived from animal faeces although an explanation for the observed value range could not be determined.

Unraveling biogeochemical phosphorus dynamics in hyperarid Mars‐analogue soils using stable oxygen isotopes in phosphate

“…The phosphate in solution was converted to Ag 3 PO 4 by adding 7 ml of Ag‐ammine solution, and the precipitate was oven‐dried at 50°C. This method does not use the DAX‐8 resin step of Tamburini et al (2010) as this is not necessary unless organic contamination is present in the subsequent Ag 3 PO 4 (Granger et al, 2018).…”

“…• Microbial P, extracted from 100 g of fresh soil with 12.5 ml of hexanol in 1 L of 18.2 μΩ ultrapure water with one 125 mm x 125 mm pre-conditioned anion-exchange resin strip. This extraction captured the mixture of inorganic (resin-P as above) and microbial phosphate (Granger et al, 2018;Kouno, Tuchiya, & Ando, 1995;Mclaughlin, Alston, & Martin, 1986). Microbial P was calculated by subtracting resin-P from hexanol-extractable P.…”

“…These biological processes include the following: (a) microbial P uptake, with ε of about −3‰ (Blake et al, 2005; Gross et al, 2015); (b) phosphoester hydrolysis by various types of phosphoenzymes (e.g., alkaline and acid phosphatase, DNase, RNase, 5'‐nucleotidase, and phytases), with ε varying between −30 and + 20‰ (Liang & Blake, 2006, 2009; von Sperber, Kries, Tamburini, Bernasconi, & Frossard, 2014); and (c) microbial hydrolysis of diphosphate by inorganic pyrophosphatase, with ε as defined by Eq. (4) at equilibration with water and soil temperature (Figure 1) (Chang & Blake, 2015; Granger et al, 2018; Pistocchi et al, 2017). where Eδ 18 O PO4 is the 18 O/ 16 O ratio of phosphate at equilibration with water catalyzed by inorganic pyrophosphatase, T is temperature in °C, and δ 18 O H2O is the δ 18 O of ambient water.…”

“…Hypothetical phosphorus cycle in a hyperarid environment (P i , inorganic P; P o , organic P; Eε, isotopic enrichment factor at equilibration with water) with ε as defined by Eq. (4) at equilibration with water and soil temperature ( Figure 1) (Chang & Blake, 2015;Granger et al, 2018;Pistocchi et al, 2017).…”

Methodology and validation of a new tandem mass spectrometer method for the quantification of inorganic and organic 18O-phosphate species

“…In comparison to IRMS, ESI is a soft ionization MS technique that generates minimal fragmentation to the gas phase molecule, allowing for structural information [66]. Soils require substantial δ 18 O characterization as isotopic values vary both temporally and spatially; therefore, individual sources of P i within each soil will possess unique signatures [67]. Co-eluting anions, such as nitrates and sulfates, and ions, like Na + and Cl -, interfere with δ 18 O analysis in P i by IRMS [49,68].…”