Timothy Ian McLaren


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McLaren

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Timothy Ian

ORCID

0000-0002-5257-7755

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2016 - 201992020 - 20247
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Publications 1 - 10 of 16
  • Phosphorus species in sequentially extracted soil organic matter fractions
    Item type: Journal Article
    Reusser, Jolanda E.; Piccolo, Alessandro; Vinci, Giovanni; et al. (2023)
    Geoderma
    The majority of organic P (Porg) in soil is considered to be part of soil organic matter (SOM) associations, but its chemical nature is largely ‘unresolved’. In this study, we investigated the Porg composition in different SOM fractions of a Gleysol soil using the Humeomics sequential chemical fractionation (SCF) procedure combined with nuclear magnetic resonance (NMR) spectroscopy. In summary, SCF procedure with subsequent NaOH-EDTA extraction of the soil residue extracted a total of 1769 mg P/kgsoil compared to 1682 mg P/kgsoil of a single-step NaOH-EDTA extraction. Approximately 38 % of the extracted Porg was present in the form of the unresolved Porg pool, which was represented by one or two underlying broad signals in the phosphomonoester region of solution 31P NMR spectra. The SCF revealed that phosphomonoesters were recovered in each fraction: 47 % of the unresolved phosphomonoesters were associated with the SOM fraction released by breaking ester bonds (40 %) and ether bonds (7 %), whereas about 30 % of this unresolved Porg pool appeared in the SOM fraction closely associated with the soil mineral phase. Furthermore, the extractability of inositol phosphates (IP) was increased from 312 mg P/kgsoil to 534 mg P/kgsoil (factor 1.7) using the SCF procedure compared to a single-step NaOH-EDTA extraction. Previous studies have reported the presence of IP in molecular size fractions greater than 10 kDa. Our findings on the removal of IP with the fractionation of the SOM could explain the presence of IP in these large associations. We demonstrate that major pools of Porg are closely associated with SOM structures, comprising a diverse array of chemical species and bonding types. These results forward our understanding of Porg stabilisation, P transformation, and P cycling in terrestrial ecosystems towards an association point of view.
  • Structural composition of organic phosphorus in hypobromite oxidised soil extracts determined by NMR spin-echo analysis
    Item type: Other Conference Item
    Reusser, Jolanda E.; Verel, René; Zindel, Daniel; et al. (2019)
  • The chemical nature of soil organic phosphorus – a critical review and global compilation of quantitative data
    Item type: Journal Article
    McLaren, Timothy Ian; Smernik, Ronald J.; McLaughlin, Michael J.; et al. (2020)
    Advances in Agronomy
    Historically, the chemical nature of organic phosphorus (P) in soil has largely been considered to comprise of recognizable biomolecules that predominantly include inositol phosphates, nucleic acids and phospholipids. However, these forms alone do not explain the existence of, or account for the processes responsible for, a larger pool of “unresolved” organic P that exists in soils. We critically reviewed the historic literature and carried out a global compilation of quantitative data to understand the chemical nature of soil organic P, including insight on what might constitute unresolved forms. We identified five key eras spanning the mid-1800s to current. Understanding of the chemical nature of organic P has largely reflected the predominant analytical technique in use, which generally involved focusing on a particular class of organic P. While inositol phosphates have been a focus throughout most eras, quantitative data reveal that the composition of the majority of organic P (typically > 50%) in soil remains unresolved. Insight on its chemical nature has revealed that it is largely comprised of phosphomonoesters (P–O–C) and is associated with large molecular weight fractions, including the soil humic acid fraction. Furthermore, there is strong evidence that this is concomitant with the existence of a broad spectral feature that appears along with sharp peaks attributable to specific compounds in the phosphomonoester region of solution 31P nuclear magnetic resonance spectra. Here, we highlight the need to improve our understanding of the chemical nature and cycling of diverse forms of organic P in soil, including that of “unresolved” pools. This will necessitate the use of multiple techniques and approaches in soil biogeochemistry that require a holistic approach to understanding soil organic matter dynamics, and the association of organic P with soil organic carbon. © 2020 Elsevier Inc.
  • Strategies for efficient phosphorus (P) use in crop and pasture systems
    Item type: Other Conference Item
    McLaughlin, MJ; McBeath, Therese M.; McLaren, Timothy Ian (2019)
  • The turnover of phosphorus in the soil solution
    Item type: Other Conference Item
    Helfenstein, Julian; Jegminat, Jannes; McLaren, Timothy Ian; et al. (2018)
    Geophysical Research Abstracts
  • Influence of cover crop residue traits on phosphorus availabiltity and subsequent uptake by plants
    Item type: Journal Article
    Honvault, Nicolas; Faucon, Michel-Pierre; McLaren, Timothy Ian; et al. (2024)
    Nutrient Cycling in Agroecosystems
    Cover crops are typically thought to increase the P nutrition of crops. However, there are mixed reports on this with some studies reporting a negative effect. An improved understanding of cover crop residues and their P release dynamics could offer new insight with the benefit of improved management for optimal P availability in cropping systems. Here, we examined the influence of cover crop residue traits for six different crop types on soil P availability and subsequent plant (ryegrass) P uptake over a four-month period in a soil with moderate P availability. Among the residue traits examined (residue P concentration, N concentration, C:P ratio, C:N ratio, N:P ratio and specific leaf area), only residue P concentration and C:P ratio were related to soil P availability and subsequent crop P uptake. Important short-term effects of residue C:P ratio on P availability were highlighted. Strong to moderate negative correlations between residue C:P ratio and subsequent crop P uptake (R2 between 0.4 and 0.8) were observed. Decreases in subsequent crop uptake of up to 43% compared to unfertilized pots occurred for residues with high C:P ratios for the first cut, strongly suggesting microbial P immobilization. Effects faded with time, with most cover crop residue additions having little to no influence on ryegrass P uptake over a four month period. Residues with the highest C:P ratio nonetheless resulted in a 22% decrease in cumulative P uptake compared to unfertilized pots. Our study highlighted that cover crop C:P ratio should be managed in order to ensure minimized adverse effects of microbial P immobilization. The observed low effects of cover crop residues on P uptake in a subsequent crop suggest that improving P availability in context with moderate P limitations via cover cropping may require relying on other services provided by cover crops such as mobilization of sparingly available P pools.
  • Dual isotopic (³³P and ¹⁸O) tracing and solution ³¹P NMR spectroscopy to reveal organic phosphorus synthesis in organic soil horizons
    Item type: Journal Article
    Siegenthaler, Maja; McLaren, Timothy Ian; Frossard, Emmanuel; et al. (2024)
    Soil Biology and Biochemistry
    Soil microorganisms can do both, mineralize and synthesize organic and condensed phosphate (P) species. Whereas P mineralization has been extensively studied, few studies have assessed the biological synthesis of organic P species, which can potentially accumulate in soil. The goal of this study was to investigate biotic and abiotic P transformations, particularly the synthesis of organic P species, upon water-soluble P addition in the organic (O) horizons of two beech forest sites with contrasting P availability. The two O horizons (low-P and high-P) were subjected to four different nutrient addition treatments (Control without addition, CN, P, and CNP additions) in an incubation experiment of up to 104 days. We combined isotopic tracing (³³P-labelled P addition and ¹⁸O-enriched soil water) into sequentially extracted P pools with the characterization of organic P species (solution ³¹P nuclear magnetic resonance (NMR) spectroscopy) and soil respiration measurements. The P availability of the two O horizons shaped the microbial response to the nutrient additions. In the low-P O horizon, P addition stimulated microbial activity together with the increase of organic (phosphodiesters and phosphonates) and condensed (polyphosphates) P species, most likely from microbial origin. In the high-P O horizon, microbes were unaffected by the added P and abiotic processes controlled its fate. CN addition had no effect on P fate in the high-P O horizon but reduced the transformation of added P into organic P and increased soil-derived P in the resin P pool in the low-P O horizon. The ¹⁸O isotopic values in phosphate of the resin P pool suggest that the released P was biologically cycled. Our study confirms with a unique multi-analytical approach the microbial synthesis of phosphodiesters, phosphonates, and polyphosphates upon inorganic P addition under low P availability.
  • Understanding the role of soil biological processes and N/P inputs in P cycling in forest ecosystems
    Item type: Other Conference Item
    Mészáros, Éva; Tamburini, Federica; Pistocchi, Chiara; et al. (2017)
  • Phosphorus desorption and isotope exchange kinetics in agricultural soils
    Item type: Journal Article
    Braun, Sabina; McLaren, Timothy Ian; Frossard, Emmanuel; et al. (2022)
    Soil Use and Management
    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 (Q1) and slowly (Q2) desorbing P, and their desorption rates k1 and k2. The amounts of isotope‐exchangeable P (E) were calculated (E1min to E>3 months) and compared with Q1 and Q2. The strongest relationship was found between E1 min and Q1 (r2 = .87, p < .01). There was also an inverse relationship between the IEK parameter n (the rate of exchange) and k1 (r2 = .52, p < .01) and k2 (r2 = .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 Q1 (P‐Olsen = 1.1 × Q1 + 2.3, r2 = .96), n and k1 were related to P‐Olsen/P‐CaCl2, while k2 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.
  • Identification of inositol phosphates (IP6, IP5 and IP4) in hypobromite oxidised soil extracts as determined by solution 31P NMR spectroscopy
    Item type: Conference Paper
    Reusser, Jolanda E.; Verel, René; Zindel, Daniel; et al. (2019)
    Geophysical Research Abstracts
Publications 1 - 10 of 16