Phosphorus (P) availability declines during ecosystem development due in part to chemical transformations of P in the soil. Here we report changes in soil P pools and the oxygen isotopic signature of inorganic phosphate (δ 18 O p ) in these pools over a 6500-year soil coastal dune chronosequence in a temperate humid environment. Total P declined from 384 to 129 mg P kg −1 during the first few hundred years of pedogenesis, due mainly to the depletion of primary mineral P in the HCl-extractable pool. The δ 18O p of HCl-extractable inorganic P initially reflected the signature of the parent material, but shifted over time towards (but not reaching) isotopic equilibrium. In contrast, δ 18 O p signatures of inorganic P extracted in water and NaHCO 3 (approximately 9 and 39 mg P kg −1 , respectively) were variable but consistent with isotopic equilibrium with soil water. In the NaOH-extractable P pool, which doubled from 63 to 128 mg P kg −1 in the early stages of pedogenesis and then gradually declined, the δ 18O p of the extracted inorganic P changed from equilibrium values early in the chronosequence to more depleted signatures in older soils, indicating greater rates of hydrolysis of labile organic P compounds such as DNA and increase involvement in P cycling as overall P availability declines through the sequence. In summary, this application of δ 18O p to a long-term soil chronosequence provides novel insight into P dynamics, indicating the importance of efficient recycling through tight uptake and mineralization in maintaining a stable bioavailable P pool during long-term ecosystem development.

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Grasslands throughout the world are responding in diverse ways to changing climate and environmental conditions. In this study we analyze indicators of phosphorus limitation including phosphorus concentrations, phosphorus to nitrogen, and carbon ratios, oxygen isotope ratios of phosphate in vegetation, and phosphatase enzyme activity in soil to shed light on potential effects of climate change on phosphorus availability to grassland vegetation. The study was conducted at the Jasper Ridge Global Change Experiment (JRGCE), California where manipulations mimicking increases in temperature, water, nitrogen and carbon-dioxide have been maintained for over 15 years. We compare our results to an earlier study conducted 3 years after the start of the experiment, in order to assess any change in the response of phosphorus over time. Our results suggest that a decade later the measured indicators show similar or only slightly stronger responses. Specifically, addition of nitrogen, the principle parameter controlling biomass growth, increased phosphorus demand but thresholds that suggest P limitation were not reached. A study documenting changes in net primary productivity (NPP) over time at the JRGCE also could not identify a progressive effect of the manipulations on NPP. Combined these results indicate that the vegetation in these grassland systems is not very sensitive to the range of climate parameters tested.

A new approach for the preparation of marine sediment samples for solution 31P nuclear magnetic resonance spectroscopy (31P NMR) has been developed and tested. This approach addresses important aspects associated with sample pretreatments for marine sediments, including the effects of sample pretreatment on sedimentary P composition. The method increases the signals of low abundance P species in 31P NMR spectra by quantitatively and precisely removing up to 80% of inorganic P (orthophosphate) from sediment samples while causing minimal alteration of the chemical structure of organic P compounds. This method uses a reductive step to solubilize P bound to iron oxyhydroxides, followed by a low pH digestion to extract P from authigenic and biogenic apatite, as well as P bound to calcium carbonate. These P forms combined represent the most abundant inorganic P reservoir in marine sediments. The sample residue is then extracted in an alkaline solvent, 0.25 M NaOH with 0.05 M Na2EDTA, and processed for 31P NMR spectroscopy. The method was tested on natural marine sediment samples from different localities with high inorganic P content (>85% molybdate reactive P), and allowed for the detection of orthophosphate monoesters and pyrophosphate in samples for which only an orthophosphate signal could be resolved with an NaOH‐EDTA extraction alone. This new approach will allow the use of 31P NMR on samples for which low organic P concentrations previously hindered the use of this tool, and will help answer longstanding question regarding the fate of organic P in marine sediments.

Phosphorus (P) plays an important role in fueling life, including microbial life in the deep subseafloor environment, which is estimated to contain up to 1% of Earth's total biomass. These microorganisms play a significant role in controlling the chemical composition of the deep ocean and atmosphere on geological timescales by selectively degrading organic matter through metabolic respiration. Consequently, understanding P geochemistry in subseafloor sediments is important, as P bioavailability can impact microbial activity. This study focuses on characterizing and quantifying the main reservoirs of solid-phase P in open-ocean sediments. The sediment samples used in this study were collected during Integrated Ocean Drilling Program (IODP) Expedition 336 to North Pond, a sediment pond located on the western flank of the Mid-Atlantic Ridge. We characterized solid-phase P reservoirs in sediments from four holes (U1384A, U1382B, U1383D, and U1383E) using the sedimentary extraction (SEDEX) sequential extraction scheme. This method quantitatively separates five distinct sedimentary P reservoirs: (1) loosely sorbed P, (2) ferric iron-bound P, (3) authigenic carbonate fluorapatite + biogenic apatite + CaCO 3 -associated P, (4) detrital apatite, and (5) refractory organic P. The separation of these P-bearing phases is based on the reactivity of each targeted phase to a particular extractant solution.