ORCID Profile
0000-0002-5257-7755
Current Organisation
University of Queensland
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Publisher: Elsevier BV
Date: 07-2019
Publisher: Springer Science and Business Media LLC
Date: 06-10-2010
Publisher: Informa UK Limited
Date: 08-06-2015
Publisher: Elsevier BV
Date: 02-2016
Publisher: Wiley
Date: 07-2012
Publisher: Wiley
Date: 07-2012
Publisher: Copernicus GmbH
Date: 21-10-2020
Abstract: Abstract. Inositol phosphates (IPs) are a major pool of identifiable organic phosphorus (P) in soil. However, insight into their distribution and cycling in soil remains limited, particularly of lower-order IP (IP5 and IP4). This is because the quantification of lower-order IP typically requires a series of chemical extractions, including hypobromite oxidation to isolate IP, followed by chromatographic separation. Here, for the first time, we identify the chemical nature of organic P in four soil extracts following hypobromite oxidation using solution 31P NMR spectroscopy and transverse relaxation (T2) experiments. Soil s les analysed include A horizons from a Ferralsol (Colombia), a Cambisol and a Gleysol from Switzerland, and a Cambisol from Germany. Solution 31P nuclear magnetic resonance (NMR) spectra of the phosphomonoester region in soil extracts following hypobromite oxidation revealed an increase in the number of sharp signals (up to 70) and an on average 2-fold decrease in the concentration of the broad signal compared to the untreated soil extracts. We identified the presence of four stereoisomers of IP6, four stereoisomers of IP5, and scyllo-IP4. We also identified for the first time two isomers of myo-IP5 in soil extracts: myo-(1,2,4,5,6)-IP5 and myo-(1,3,4,5,6)-IP5. Concentrations of total IP ranged from 1.4 to 159.3 mg P per kg soil across all soils, of which between 9 % and 50 % were comprised of lower-order IP. Furthermore, we found that the T2 times, which are considered to be inversely related to the tumbling of a molecule in solution and hence its molecular size, were significantly shorter for the underlying broad signal compared to for the sharp signals (IP6) in soil extracts following hypobromite oxidation. In summary, we demonstrate the presence of a plethora of organic P compounds in soil extracts, largely attributed to IPs of various orders, and provide new insight into the chemical stability of complex forms of organic P associated with soil organic matter.
Publisher: Elsevier BV
Date: 12-2019
Publisher: Elsevier
Date: 2020
Publisher: Elsevier BV
Date: 08-2017
Publisher: Springer Science and Business Media LLC
Date: 08-11-2019
Publisher: American Chemical Society (ACS)
Date: 31-03-2016
Abstract: Calcium phosphate (CaP) minerals may comprise the main phosphorus (P) reserve in alkaline soils, with solubility dependent on pH and the concentration of Ca and/or P in solution. Combining several techniques in a novel way, we studied these phenomena by progressively depleting P from suspensions of two soils (low P) using an anion-exchange membrane (AEM) and from a third soil (high P) with AEM together with a cation-exchange membrane. Depletions commenced on untreated soil, then continued as pH was manipulated and maintained at three constant pH levels: the initial pH (pHi) and pH 6.5 and 5.5. Bulk P K-edge X-ray absorption near-edge structure (XANES) spectroscopy revealed that the main forms of inorganic P in each soil were apatite, a second more soluble CaP mineral, and smectite-sorbed P. With moderate depletion of P at pHi or pH 6.5, CaP minerals became more prominent in the spectra compared to sorbed species. The more soluble CaP minerals were depleted at pH 6.5, and all CaP minerals were exhausted at pH 5.5, showing that the CaP species present in these alkaline soils are soluble with decreases of pH in the range achievable by rhizosphere acidification.
Publisher: Wiley
Date: 02-2021
DOI: 10.1002/HYP.14040
Abstract: Constructed wetlands (CWs) are engineered systems for treating wastewater by sequestering nutrients and contaminants. Our aim was to assess the main phosphorus (P) binding states in operating CWs to assess P saturation and indications on P recycling potential of filter materials, which might be necessary under future peak P scenarios. The investigated vertical flow CWs (operation time up to 16 years) are based on either fluviatile (Fluv) sand or zeolite‐ (Ze‐LS) and clinopyroxene (Cl‐LS)‐dominated lava sand. Organic and inorganic P accumulated in all CWs independent of filter materials and showed a considerable increase with operation time. Concentrations of P decreased sharply with depth in the Fluv‐CWs compared to only a slight decrease in the lava sand CWs, with P concentrations of deeper horizons approximating the relatively P enriched original lava sand substrates. Orthophosphate was the dominant pool in all CWs, while the sum of organic fractions ranged between 11% and 33%. Sequential extraction indicated that P was mainly associated with Fe and Al (hydr)oxides for Fluv‐CWs and Ze‐LS‐CWs, while Ca and Mg bound mineral phosphates dominated in Cl‐LS‐CWs. Oxalate extractions pointed to a clear dominance of P fractions associated with poorly crystalline Fe‐ and Al‐(oxy)hydroxides. Solution 31 P NMR analyses revealed that inositol hexakisphosphates were a major pool of organic P in surface layers of CWs, which increased with operation time. With a maximum of 0.5% P content, filter sands do not appear to be a suitable fertilizer for direct application to agricultural fields. The dominance of inorganic, poorly crystalline P species point to potentially high desorption capacity which might be investigated further, to assess recycling potential of P or usage of filter materials as soil amendments with relatively high plant available P. The latter might become feasible and economically attractive under future P scarcity. Simultaneously, P saturation indexes (DPS) did not indicate an imminent P saturation of filters, since P accumulation was not restricted by binding to Al and Fe minerals.
Publisher: CSIRO Publishing
Date: 2013
DOI: 10.1071/CP13025
Abstract: Recent studies report low and variable phosphorus (P) fertiliser use efficiency (PUE) for cotton in the northern grains region (NGR) of eastern Australia. This may be due to cotton accessing P pools that are not currently tested for in the subsoil (10–30 cm) or variation in response to P source and placement strategy. Two glasshouse studies were used to investigate this, incorporating two soil P tests to assess readily and slowly available P pools (Colwell, and a dilute acid colloquially referred to as the BSES extractant), and five different P fertiliser placement strategies in the subsoil. Eighteen Vertosols were collected across southern to central Queensland in the NGR, and then used to grow faba bean (Vicia faba L.) and cotton (Gossypium hirsutum L.) sequentially in the same 28-L pot. Readily available P pools assessed by Colwell-P were of major importance for faba bean and cotton dry matter, as well as for tissue P concentrations. Cotton was less responsive to extractable subsoil P concentrations than faba bean, suggesting either greater internal PUE or improved ability to accumulate P under conditions of limited availability. We recommend that subsoil P fertilisation should occur before sowing faba bean to maximise PUE in a cotton–faba bean rotation. Faba bean and cotton both recovered more P when the subsoil was fertilised, but no in idual P fertiliser placement strategy was superior. Phosphorus extracted using the BSES method was not correlated with faba bean or cotton dry matter or tissue P concentration over the single crop cycle. We also recommend that Colwell-P be measured in the topsoil and subsoil to understand the quantity of plant-available P in Vertosols of the NGR, and that further research is needed to describe the resupply of the readily available P pool from slowly available P pools during a single crop cycle.
Publisher: Elsevier BV
Date: 12-2015
Publisher: Elsevier BV
Date: 2023
Publisher: Springer Science and Business Media LLC
Date: 02-12-2018
Publisher: Wiley
Date: 23-04-2014
DOI: 10.1111/AEN.12086
Publisher: Wiley
Date: 21-11-2016
Publisher: Springer Science and Business Media LLC
Date: 23-05-2018
Publisher: Wiley
Date: 29-09-2014
Publisher: American Chemical Society (ACS)
Date: 16-08-2019
Abstract: Acid-soluble soil phosphorus (P) is a potential resource in P-limited agricultural systems that may become critical as global P sources decrease in the future. The fate of P in three alkaline Vertisols, a major agricultural soil type, after acidic incubation was investigated using synchrotron-based K-edge X-ray absorption near-edge structure (XANES) spectroscopy, geochemical modeling, wet chemistry soil extraction, and a P sorption index. Increases in labile P generally coincided with decreased stability and dissolution of calcium phosphate (CaP) minerals. However, only a minor proportion of the CaP dissolved in each soil was labile. In two moderate-P soils (800 mg P kg
Publisher: Wiley
Date: 25-06-2015
Publisher: Wiley
Date: 2014
Publisher: Oxford University Press (OUP)
Date: 20-02-2021
Abstract: Rock phosphate is an alternative form of phosphorus (P) fertilizer however, there is no information regarding the influence of P fertilizer sources in Brazilian Cerrado soils upon microbial genes coding for phosphohydrolase enzymes in crop rhizospheres. Here, we analyze a field experiment comparing maize and sorghum grown under different P fertilization (rock phosphate and triple superphosphate) upon crop performance, phosphatase activity and rhizosphere microbiomes at three levels of ersity: small subunit rRNA marker genes of bacteria, archaea and fungi a suite of alkaline and acid phosphatase and phytase genes and ecotypes of in idual genes. We found no significant difference in crop performance between the fertilizer sources, but the accumulation of fertilizer P into pools of organic soil P differed. Phosphatase activity was the only biological parameter influenced by P fertilization. Differences in rhizosphere microbiomes were observed at all levels of bio ersity due to crop type, but not fertilization. Inspection of phosphohydrolase gene ecotypes responsible for differences between the crops suggests a role for lateral genetic transfer in establishing ecotype distributions. Moreover, they were not reflected in microbial community composition, suggesting that they confer competitive advantage to in idual cells rather than species in the sorghum rhizosphere.
Publisher: Springer Science and Business Media LLC
Date: 30-07-2015
Publisher: CSIRO Publishing
Date: 2017
DOI: 10.1071/SR16058
Abstract: Few studies have considered the influence of climate on organic phosphorus (P) speciation in soils. We used sodium hydroxide–ethylenediaminetetra-acetic acid (NaOH–EDTA) soil extractions and solution 31P nuclear magnetic resonance spectroscopy to investigate the soil P composition of five alpine and sub-alpine soils. The aim was to compare the P speciation of this set of soils with those of soils typically reported in the literature from other cold and wet locations, as well as those of other Australian soils from warmer and drier environments. For all alpine and sub-alpine soils, the majority of P detected was in an organic form (54–66% of total NaOH–EDTA extractable P). Phosphomonoesters comprised the largest pool of extractable organic P (83–100%) with prominent peaks assigned to myo- and scyllo-inositol hexakisphosphate (IP6), although trace amounts of the neo- and d-chiro-IP6 stereoisomers were also present. Phosphonates were identified in the soils from the coldest and wettest locations α- and β-glycerophosphate and mononucleotides were minor components of organic P in all soils. The composition of organic P in these soils contrasts with that reported previously for Australian soils from warm, dry environments where inositol phosphate (IP6) peaks were less dominant or absent and humic-P and α- and β-glycerophosphate were proportionally larger components of organic P. Instead, the soil organic P composition exhibited similarities to soils from other cold, wet environments. This provides preliminary evidence that climate is a key driver in the variation of organic P speciation in soils.
Publisher: Royal Society of Chemistry (RSC)
Date: 2020
DOI: 10.1039/C9EM00485H
Abstract: Inositol phosphates, particularly myo -inositol hexakisphosphate ( myo -IP 6 ), are an important pool of soil organic phosphorus (P) in terrestrial ecosystems.
Publisher: Elsevier BV
Date: 04-2022
Publisher: American Chemical Society (ACS)
Date: 30-10-2015
Abstract: Phosphorus (P) is an essential element for life, an innate constituent of soil organic matter, and a major anthropogenic input to terrestrial ecosystems. The supply of P to living organisms is strongly dependent on the dynamics of soil organic P. However, fluxes of P through soil organic matter remain unclear because only a minority (typically 10 kDa) was markedly different to that of the low molecular weight fraction (<10 kDa). The former was dominated by a broad peak, which is consistent with P bound by phosphomonoester linkages of supra-/macro-molecular structures, whereas the latter contained all of the sharp peaks that were present in unfractionated extracts, along with some broad signal. Overall, phosphomonoesters in supra-/macro-molecular structures were found to account for the majority (61% to 73%) of soil organic P across the five erse soils. These soil phosphomonoesters will need to be integrated within current models of the inorganic-organic P cycle of soil-plant terrestrial ecosystems.
Publisher: Copernicus GmbH
Date: 08-01-2018
Abstract: Abstract. The exchange rate of inorganic phosphorus (P) between the soil solution and solid phase, also known as soil solution P turnover, is essential for describing the kinetics of bioavailable P. While soil solution P turnover (Km) can be determined by tracing radioisotopes in a soil–solution system, few studies have done so. We believe that this is due to a lack of understanding on how to derive Km from isotopic exchange kinetic (IEK) experiments, a common form of radioisotope dilution study. Here, we provide a derivation of calculating Km using parameters obtained from IEK experiments. We then calculated Km for 217 soils from published IEK experiments in terrestrial ecosystems, and also that of 18 long-term P fertilizer field experiments. Analysis of the global compilation data set revealed a negative relationship between concentrations of soil solution P and Km. Furthermore, Km buffered isotopically exchangeable P in soils with low concentrations of soil solution P. This finding was supported by an analysis of long-term P fertilizer field experiments, which revealed a negative relationship between Km and phosphate-buffering capacity. Our study highlights the importance of calculating Km for understanding the kinetics of P between the soil solid and solution phases where it is bioavailable. We argue that our derivation can also be used to calculate soil solution turnover of other environmentally relevant and strongly sorbing elements that can be traced with radioisotopes, such as zinc, cadmium, nickel, arsenic, and uranium.
Publisher: Elsevier BV
Date: 11-2015
Publisher: Elsevier BV
Date: 2023
Publisher: Springer Science and Business Media LLC
Date: 21-03-2023
DOI: 10.1007/S10956-023-10027-2
Abstract: Self-report assessments are used frequently in higher education to assess a variety of constructs, including attitudes, opinions, knowledge, and competence. Systems thinking is an ex le of one competence often measured using self-report assessments where in iduals answer several questions about their perceptions of their own skills, habits, or daily decisions. In this study, we define systems thinking as the ability to see the world as a complex interconnected system where different parts can influence each other, and the interrelationships determine system outcomes. An alternative, less-common, assessment approach is to measure skills directly by providing a scenario about an unstructured problem and evaluating respondents’ judgment or analysis of the scenario (scenario-based assessment). This study explored the relationships between engineering students’ performance on self-report assessments and scenario-based assessments of systems thinking, finding that there were no significant relationships between the two assessment techniques. These results suggest that there may be limitations to using self-report assessments as a method to assess systems thinking and other competencies in educational research and evaluation, which could be addressed by incorporating alternative formats for assessing competence. Future work should explore these findings further and support the development of alternative assessment approaches.
Publisher: Wiley
Date: 06-01-2021
DOI: 10.1002/SAJ2.20347
Abstract: The majority of soil organic P is typically that of “unresolved” phosphomonoesters, which are associated with organic P (Po) in large molecular weight (MW) fractions. However, the composition of this pool of Po remains unclear and could contain more than one component. Our aim was to identify the number and nature of components in soil extracts of different MW using solution 31 P nuclear magnetic resonance (NMR) spectroscopy and spectral deconvolution fitting. Three surface soils were collected from native sites, which were extracted for Po using 0.25 M NaOH + 0.05 M Na 2 –EDTA (unfractionated), followed by size separation using ultrafiltration, resulting in four MW fractions ( kDa, kDa, kDa and kDa, and kDa). The NMR analyses revealed a ersity of Po species in all MW fractions across the three soils. In particular, the phosphomonoester region of the ‐kDa fraction comprised up to 10 components of varying linewidth (0.5–18.6 Hz) and a broad signal (228 Hz). This broad signal was also present in the ‐kDa fraction, albeit at a lower concentration (average was 29% of that in the unfractionated extracts). Furthermore, solution 31 P NMR spectra on the ‐kDa fraction revealed a ersity of sharp signals (up to 28) in the phosphomonoester region. Overall, our findings show that soil phosphomonoesters in large MW fractions comprise multiple components of varying linewidth.
Publisher: Wiley
Date: 17-11-2020
DOI: 10.1111/SUM.12674
Abstract: To improve phosphorus (P) fertilization and environmental assessments, a better understanding of release kinetics of solid‐phase P to soil solution is needed. In this study, Fe (hydr)oxide‐coated filter papers (Fh papers), isotopic exchange kinetics (IEK) and chemical extractions were used to assess the sizes of fast and slowly desorbing P pools in the soils of six long‐term Swedish field experiments. The P desorption data from the Fh‐paper extraction of soil (20 days of continual P removal) were fitted with the Lookman two‐compartment desorption model, which estimates the pools of fast (Q 1 ) and slowly (Q 2 ) desorbing P, and their desorption rates k 1 and k 2 . The amounts of isotope‐exchangeable P (E) were calculated (E 1min to E months ) and compared with Q 1 and Q 2 . The strongest relationship was found between E 1 min and Q 1 ( r 2 = .87, p .01). There was also an inverse relationship between the IEK parameter n (the rate of exchange) and k 1 ( r 2 = .52, p .01) and k 2 ( r 2 = .52, p .01), suggesting that a soil with a high value of n desorbs less P per time unit. The relationships between these results show that they deliver similar information, but both methods are hard to implement in routine analysis. However, Olsen‐extractable P was similar in magnitude to Q 1 (P‐Olsen = 1.1 × Q 1 + 2.3, r 2 = .96), n and k 1 were related to P‐Olsen/P‐CaCl 2 , while k 2 was related to P‐oxalate/P‐Olsen. Therefore, these extractions can be used to estimate the sizes and desorption rates of the different P pools, which could be important for assessments of plant availability and leaching.
Publisher: Elsevier BV
Date: 03-2019
No related grants have been discovered for Timothy McLaren.