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Colloid-bound and dissolved phosphorus species in topsoil water extracts along a grassland transect from Cambisol to Stagnosol

Jiang, X., Bol, R., Cade-Menun, B.J., Nischwitz, V., Willbold, S., Bauke, S., Vereecken, H., Amelung, W., Klumpp, E. (2017). Colloid-bound and dissolved phosphorus species in topsoil water extracts along a grassland transect from Cambisol to Stagnosol, 14(5), 1153-1164. http://dx.doi.org/10.5194/bg-14-1153-2017

Abstract

© 2017 Author(s). Phosphorus (P) species in colloidal and "dissolved" soil fractions may have different distributions. To understand which P species are potentially involved, we obtained water extracts from the surface soils of a gradient from Cambisol, Stagnic Cambisol to Stagnosol from temperate grassland in Germany. These were filtered to <450 nm, and divided into three procedurally defined fractions: small-sized colloids (20-450 nm), nano-sized colloids (1- 20 nm), and "dissolved P" (<1 nm), using asymmetric flow field-flow fractionation (AF4), as well as filtration for solution 31P-nuclear magnetic resonance (NMR) spectroscopy. The total P of soil water extracts increased in the order Cambisol<Stagnic Cambisol<Stagnosol due to increasing contributions from the dissolved P fraction. Associations of C-Fe/Al-PO3-4 /pyrophosphate were absent in nanosized (1-20 nm) colloids from the Cambisol but not in the Stagnosol. The 31P-NMR results indicated that this was accompanied by elevated portions of organic P in the order Cambisol>Stagnic Cambisol>Stagnosol. Across all soil types, elevated proportions of inositol hexakisphosphate (IHP) species (e.g., myo-, scyllo- and D-chiro-IHP) were associated with soil mineral particles (i.e., bulk soil and small-sized soil colloids), whereas other orthophosphate monoesters and phosphonates were found in the "dissolved" P fraction. We conclude that P species composition varies among colloidal and "dissolved" soil fractions after characterization using advanced techniques, i.e., AF4 and NMR. Furthermore, stagnic properties affect P speciation and availability by potentially releasing dissolved inorganic and esterbound P forms as well as nano-sized organic matter-Fe/Al-P colloids.

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