Sample pretreatment and phosphorus speciation in wetland soils

Abstract

We assessed the infl uence of sample pretreatment on the amounts and forms of P extracted in NaOH"CEDTA (ethylenediamine tetraacetic acid) from a series of contrasting wetland soils from the Florida Everglades. Samples of unconsolidated benthic fl oc and underlying soil (0"C10 cm) were extracted either fresh (overnight refrigeration only), air dried (10 d at ¡«30¡aC), or frozen at "C80¡aC and lyophilized (¡«48 h), before extraction and solution 31P nuclear magnetic resonance (NMR) spectroscopy. Signifi cant differences in total P extraction following pretreatment were detected for one out of four benthic fl oc 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 31P 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 fl oc, despite representing an important component of the organic P extracted from dried samples. The apparent sample-specifi c nature of the changes confi rms the importance of carefully assessing pretreatment effects in studies of soil organic P in wetlands.