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At the early stages of pedogenesis, the dynamics of phosphorus (P) in soils are controlled by microbial communities, the physicochemical properties of the soil and the environmental conditions. While various microorganisms involved in carrying out biogeochemical processes have been identified, little is known about the actual contribution of microbial processes, such as organic P hydrolysis and microbial P turnover, to P cycling. We thus focused on processes driven by microbes and how they affect the size and cycling of organic and inorganic soil P pools along a soil chronosequence in the Chamser Kangri glacier forefield (Western Himalayas). The rapid retreat of the glacier allowed us to study the early stages of soil formation under a cold arid climate. Biological P transformations were studied with the help of the isotopic composition of oxygen (O) in phosphate (δ18OP) coupled to sequential P fractionation performed on soil samples (0-5gcm depth) from four sites of different age spanning 0 to 100-150 years. The P bound to Ca, i.e., 1gM HCl-extractable P, still represented 95g% of the total P stock after approximately 100 years of soil development. Its isotopic composition was similar to the parent material at the most developed site. Primary phosphate minerals, possibly apatite, mostly comprised this pool. The δ18OP of the available P and the NaOH-extractable inorganic P instead differed from that of the parent material, suggesting that these pools underwent biological turnover. The δ18OP of the available P was mostly controlled by the microbial P, suggesting fast exchanges occurred between these two pools possibly fostered by repeated freezing-thawing and drying-rewetting cycles. The release of P from organic P becomes increasingly important with soil age, constituting one-third of the P flux to available P at the oldest site. Accordingly, the lighter isotopic composition of the P bound to Fe and Al oxides at the oldest site indicated that this pool contained phosphate released by organic P mineralization. Compared to previous studies on early pedogenesis under alpine or cold climate, our findings suggest a much slower decrease of the P-bearing primary minerals during the first 100 years of soil development under extreme conditions. However, they provide evidence that, by driving short-term P dynamics, microbes play an important role in controlling the redistribution of primary P into inorganic and organic soil P pools., Soil, 8 (1), ISSN:2199-3971, ISSN:2199-398X

Phosphorus (P) fertilizers are known to increase crop productivity; however, when applied in excess, it can cause serious environment pollution. Monitoring P pollution in natural environments using stable isotopes has been difficult because P has only one stable isotope (31P) making the use of P stable isotope tracing not an option. Radioactive P isotopes (32P and 33P) have been used but its drawbacks are the short half-life, health risks and safety procedures required to apply them in agricultural catchments. Phosphorus in organic and inorganic P forms is strongly bonded to oxygen (O), which has three stable isotopes, providing a system to track P cycling in agricultural catchments and environment using the stable isotopes of O in phosphate (δ18O-PO4). In recent years, various studies have indicated that the analysis of the stable isotopic composition of oxygen (O) bound to P (δ18Op) to better understand P cycling in the environment, has become a promising tracer (surrogate) to investigate soil P transformation, plant P uptake and to trace the sources of P from the soil to water bodies and the environment. The chapter outlines the background and examples of δ18Op studies in sediments, soils, fresh water, mineral fertilizers and plants., Oxygen Isotopes of Inorganic Phosphate in Environmental Samples, ISBN:978-3-030-97496-1, ISBN:978-3-030-97497-8

The five stepwise purification of extracts and final precipitation of silver phosphate (A1–A5) are described. The first two steps (A1 and A2) are removing organic matter and are concentrating the phosphate in the extract by reducing the volume. Certain cations could interfere with the precipitation of silver phosphate and are removed in step A3. Silver chloride, which, if not removed, could co-precipitate with silver phosphate, is removed in step A4. The final analyte is then precipitated in step A5. The filtration steps can be quite tedious, using vacuum filtration equipment is therefore recommended. Following step A5, the silver phosphate samples need to be weighed in for the measurement with a thermal conversion elemental analyser (TC/EA) coupled to a continuous-flow isotope-ratio mass spectrometer (IRMS)., Oxygen Isotopes of Inorganic Phosphate in Environmental Samples, ISBN:978-3-030-97496-1, ISBN:978-3-030-97497-8

Studies showed that the δ18OP is a useful tool to study P in the environment. Adequate extraction protocols for the targeted P pools of the study are a prerequisite for a successful study. Likewise, for most environmental samples, including water, soil, sediment and plant samples, it is crucial that the samples are processed as soon as possible after they have been taken to avoid any alterations of the original δ18OP signature. This is especially true when more bioavailable P pools, like soluble reactive P (SRP) in water samples, are extracted and analysed. Brucite precipitation of water samples should be directly done in the field, fresh soil and sediment samples have to be extracted within 7 days (if microbial P is targeted, on the day of sampling), and plant samples have to be extracted within a few hours of sampling or be frozen. The chapter briefly describes the P cycle in aquatic and terrestrial ecosystems and give an overview about extracting the most common P pools for δ18OP analysis: soluble reactive P in water samples, sequentially extracted P pools of soil, sediment, fertilizer and plant samples., Oxygen Isotopes of Inorganic Phosphate in Environmental Samples, ISBN:978-3-030-97496-1, ISBN:978-3-030-97497-8

Current understanding of phosphorus (P) dynamics is mostly based on experiments carried out under steady-state conditions. However, drying-rewetting is an inherent feature of soil behavior, and as such also impacts P cycling. While several studies have looked at net changes in P pool sizes with drying-rewetting, few studies have dynamically tracked P exchange using isotopes, which would give insights on P mean residence times in a given pool, and thus P availability. Here, we subjected three soils from a climatic gradient on the Kohala peninsula from Hawaii to 5-month drying-rewetting treatments. The hypotheses were that physico-chemical and biotic processes would be differently affected by repeated drying-rewetting cycles, and that response would depend on climatic history of the soils. Soils were labeled with 33P and 18O enriched water. At select time intervals, we carried out a sequential extraction and measured P concentration, 33P recovery (only first 3 months), and incorporation of 18O from water into phosphate. This allowed tracing P dynamics in sequentially extracted pools as well as O dynamics in phosphate, which are driven by biological processes. Results showed that P concentration and 33P recovery were predominantly driven by soil type. However, across all soils we observed faster dilution of 33P from resin-P into less mobile inorganic pools under drying-rewetting. On the other hand, O dynamics in phosphate were mostly governed by drying-rewetting treatment. Under drying-rewetting, considerably less O was incorporated from water into phosphate of resin-P, microbial-P and HCl-P, suggesting that drying-rewetting reduced biological P cycling. Hence, our results suggest that repeated drying-rewetting increases inorganic P exchange while reducing biological P cycling due to reduced microbial activity, independent of climatic history of the soils. This needs to be considered in P management in ecosystems as well as model representations of the terrestrial P cycle., Frontiers in Soil Science, 1, ISSN:2673-8619