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

Abstract

Phosphorus cycling influences productivity and diversity in tropical wetlands, yet little is known about the forms of P found in the accreting organic matter of these ecosystems. We used alkaline (NaOH-ethylenediamine tetraacetic acid [EDTA]) extraction and solution ^^P nuclear magnetic resonance (NMR) spectroscopy to characterize P in surface soils across a strong nutrient gradient within a tropical omhrotrophic peat dome. From the interior bog plain to the marginal Raphia taedigera swamp, total soil P increased from 14.6 to 70.9 g m"-^ and resin-extractable P from 0.1 to 30 mg kg~^ Phosphatase activity declined across the same transect (364-46 jxmol methylumbelliferone kg~^ min~'), indicating an increase in P availability toward the periphery of the wetland. Organic P identified hy solution ^^P NMR spectroscopy included phosphomonoesters (12-17%), phosphodiesters (10-14%), and phosphonates (up to 3.3% of total P). Inositol phosphates were not detected in these acidic peats. Inorganic P forms included orthophosphate (9-25% of total P), pyrophosphate (up to 3%), and long-chain polyphosphates; the latter occurred in concentrations (up to 24% of total soil P) considerably higher than previously found in wetland soils. The concentration of residual (unextractable) P was similar among sites (mean 280 mg kg~^), resulting in an increase in its proportion of the total soil P from 29% at the P-rich margins to 55% at the P-poor interior. This is the first information on the P composition of tropical wetland soils and provides a basis for further study of the cycling and contribution of P forms to the nutrition of plants and microorganisms.Abbreviations: AEM, anion exchange membrane; EDTA, ethylenediamine tetraacetic acid; NMR, nuclear magnetic resonance. P bospborus is a key clement limiting ecosystem processes in freshwater wetlands (Daniel et al., 1998;Rejmánková, 2001). Because mucb of tbe P in wetland soils occurs in organic forms (Davelaar, 1993;Newman and Robinson, 1999;Reddy et al., 2005), P availability is dependent on tbe cycling of P from biological material. Biologically derived P in soils, however, represents a variety of compounds that differ markedly in their behavior and bioavailability (Celi and Barberis, 2005;Condron et al, 2005). The nature of these P forms is the result of the dynamic interplay among biological inputs (Makarov et al., 2005), abiotic stabilization (Celi and Barberis, 2005), and biological modification (Cheesman et al, 2010b), all ofwhich are influenced by edaphic, environmental, and biological factors. Information on the role these factors have in determining P composition in wetland soils is therefore critical for understanding the cycling and productivity of wetland systems, as well as in explaining future responses to perturbations.Unlike quantitative extraction and determination of P pools based on chemical stability, techniques such as solution P NMR spectroscopy allow the assessment of actual P forms present in environmental samples (Cade-Menun, 2005;McKelvie, 2005;. This has yield...

Speciation and distribution of P associated with Fe and Al oxides in aggregate-sized fraction of an arable soil

“…A similar extraction efficiency (average of 63 % of total P) was found in a recent study of dried wetland soil samples (Cheesman et al, 2012). Inorganic and organic P contents in NaOH-Na 2 EDTA extracts were characterized by solution 31 P-NMR spectroscopy.…”

“…Our study aims to provide a novel method to understand the distribution of Pi and Po on Fe/Al oxides in the alkaline extract of soil. Furthermore, the residual P after alkaline extraction still accounts for significant proportion of P for some soils, most apparent in highpH soil or for unamended soils with low P concentration Cheesman et al, 2012;McDowell et al, 2007;Turner et al, 2007;Turner et al, 2003). The residual P is by definition unidentified and is simply presumed to be recalcitrant in the environment (Cheesman et al, 2010).…”

Long-term macronutrient stoichiometry of UK ombrotrophic peatlands

“…Gorham and Janssens (2005) observed progressive depletion of P (and N) content with distance from the cultivated Midwest, and attribute this to transport of nutrients as a component of windblown dust (Neff et al, 2008;Ravi et al, 2011;Van Pelt and Zobeck, 2007). Cheesman et al (2012) demonstrate that P availability decreases along a transect from a swamp-rimmed ombrotrophic wetland in Panama towards its centre, consistent with declining lateral supply (Tipping et al, 2014) with distance from neighbouring forest ecosystems. In the UK, increased inputs of P via dust and biological debris may be especially prevalent, due both to the proximity of many of its bogs to agricultural land, and to the magnitude of agricultural intensification over recent centuries.…”

Organic phosphorus in the aquatic environment

“…Phosphonates appear to be less prevalent in freshwater ecosystems compared to marine systems. [72,[113][114][115][116][117] Biogeochemistry Like phospholipids, little is known about the biogeochemical cycling of phosphonates in aquatic ecosystems. [102] Although often assumed to be recalcitrant, recent molecular studies have shown that a diverse range of freshwater and marine bacteria and phytoplankton have genes associated with the production of hydrolytic enzymes capable of catalysing the breakdown of phosphonates.…”