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BACKGROUND AND AIMS: Despite the recognised importance of root architecture to plant productivity, our ability to easily observe and quantify root responses to stresses in soil at appropriate mechanistic resolution, remains poor. In this study we examine the impact of P bands on root architecture in heterogeneous soil, trialling a rapid non-destructive analysis technique. METHODS: We examined fast (<5 min), high resolution (69 μm voxels) x-ray tomography (μCT) to non-destructively observe and quantify wheat (Triticum aestivum L.) roots in a repacked Oxisol, in 3D, with and without a band of P-enriched soil. RESULTS: We found that wheat roots displayed localised responses (were plastic) and responded with additional root length within the banded P fertiliser. The seedling root systems also altered 3D root architecture in the band by increasing the number and length of branch roots. Branch root angle was not altered by the P band. The spatial precision of the branching response was striking and raises questions concerning the root sensing and/or response mechanisms.

Summary The mechanisms controlling the genesis of rhizosheaths are not well understood, despite their importance in controlling the flux of nutrients and water from soil to root. Here, we examine the development of rhizosheaths from drought‐tolerant and drought‐sensitive chickpea varieties; focusing on the three‐dimensional characterization of the pore volume (> 16 μm voxel spatial resolution) obtained from X‐ray microtomography, along with the characterization of mucilage and root hairs, and water sorption. We observe that drought‐tolerant plants generate a larger diameter root, and a greater and more porous mass of rhizosheath, which also has a significantly increased water sorptivity, as compared with bulk soil. Using lattice Boltzmann simulations of soil permeability, we find that the root activity of both cultivars creates an anisotropic structure in the rhizosphere, in that its ability to conduct water in the radial direction is significantly higher than in the axial direction, especially in the drought‐tolerant cultivar. We suggest that significant differences in rhizosheath architectures are sourced not only by changes in structure of the volumes, but also from root mucilage, and further suggest that breeding for rhizosheath architectures and function may be a potential future avenue for better designing crops in a changing environment.

Portable X-ray fluorescence (PXRF) can provide a rapid and nondestructive analysis for environmentally important elements in plant matrices. No previous publication has been able to demonstrate the application of PXRF element determination in plant material. To assess the applicability of PXRF for total element analysis, four plant species of agricultural importance {corn (maize) [Zea mays L.], cotton [Gossypium hirsutum L.], soybean [Glycine max (L.) Merr.], and wheat [Triticum aestivum L.]} were collected across northern New South Wales (NSW), Australia. The effect of scanning time and particle size on data quality was also evaluated. For three plant species (corn, cotton, and soybean) there were significant linear relationships between the acid digest values and the PXRF readings for Ca, Co, Cr, Fe, K, Mn, Ni, P, S, Si, and Zn. Only slight reductions in the regression coefficient (r2) for Fe and Zn were observed in cotton when scanning time was reduced by more than half. Similar regressions between corn and cotton at 120 s demonstrated the potential for a single algorithm for plant matrices. The use of novel techniques to optimize PXRF settings for quantitative determination of total plant elements provides an efficient alternative to traditional plant digestion.

Spatio-temporal development of the rhizosheath during root elongation has the potential to modify the function of the rhizosphere under abiotic stress. We quantified the impact of carbon (i.e. glucose) addition on the development and function of rhizosheath of drought tolerant and sensitive chickpea ( Cicer arietinum L.) by integrating soil pore volume obtained from X-ray microtomography (µCT), soil physical and microbial respiration measures, and measurements of root traits. Structural equation modelling indicated the feedback mechanisms between added carbon, root traits, pore geometry, and soil functions differed between the cultivars in a fashion congruent with the concept of soil as a self-organising system that interacts with an introduced root system. The drought tolerant cultivar partitioned more photosynthetically fixed carbon to the roots, had more root hairs and more porous rhizosheath, as compared with the sensitive cultivar.

We conducted acute toxicity studies using semi-static protocols to examine the lethal responses of Australian bass and silver perch exposed to antimony (Sb) oxidation states in Sb(III) (10.5–30.5 mg L−1) and Sb(V) (95.9–258.7 mg L−1). Bioavailability and the effects of Sb on body ion regulation (Na, Ca, Mg, and K) were also investigated. Antimony species-specific effects were observed with exposure to both Sb oxidation states. Median lethal concentrations (LC50s) for Sb(III) were 13.6 and 18 mg L−1 for Australian bass and silver perch, respectively, and the LC50 for Sb(V) in Australian bass was 165.3 mg L−1. The LC50 could not be calculated for silver perch exposed to Sb(V) as the maximum exposure concentrations produced 40% mortality but a larger-than value of > 258.7 mg L−1 was estimated. Relative median potency values derived from the LC50s were 0.1 Sb(III) and 12.2 and 16.6 Sb(V) for Australian bass and silver perch, respectively, demonstrating greater toxicity of Sb(III) to both fish species. Antimony uptake in fish was observed. Median critical body residue (CBR50) values of 77.7 and 26.6 mg kg−1 for Sb(III) were estimated for Australian bass and silver perch, respectively, and 628.1 mg kg−1 for Sb(V) in Australian bass. Bioconcentration factors (BCFs) for both Sb(III) and Sb(V) did not change with exposure but the greater BCFs for fish exposed to Sb(III) indicate that it is more bioavailable than Sb(V) in acute exposure. No effects on whole-body Na, Ca, Mg, or K ions were observed with fish exposure to either Sb species.

This study reports on a wide-scale, systematic sampling program over two consecutive years investigating As and Cd and associated implications for human health in farming areas of the dry zone, Sri Lanka, where chronic kidney disease with unknown etiology (CKDu) is endemic. Surface soil (0–15 cm), fertilizer and rice seed samples were collected in 2017 and 2018 from three CKDu affected areas [Medawachchiya (M), Padaviya (P) and Giradurukotte (G)], and a non-affected control site [Hambanthota (H)]. All inorganic fertilizer samples showed low As (< 30 mg kg −1 ) and Cd (< 1.25 mg kg −1 ) concentrations, less than European Union guideline values, and no correlation with soil concentrations. Arsenic (≤ 3.8 mg kg −1 ) and Cd (≤ 3.0 mg kg −1 ) in the 400 soil samples analyzed were low at all four locations, and soils were considered suitable for sensitive and agricultural use. A human health risk assessment demonstrated the As and Cd concentrations in surface soil provided no concern for non-carcinogenic risk, and negligible or acceptable carcinogenic risk for all locations sampled. The As and Cd in rice seeds harvested were also less than detection limits (< 0.1 mg kg −1 ). This work provides clarity around As and Cd baseline values in certain farm soils of the dry zone Sri Lanka, and no substantive evidence that the levels of As and Cd in the surface soils contribute to CKDu in local agricultural populations. Additional sampling of subsurface soil and water resources would satisfy some uncertainties with the risk assessment described. Graphic Abstract

Portable X-ray fluorescence (PXRF) spectrometry can provide rapid and nondestructive analyses of agriculturally important elements in soil. To assess the applicability of PXRF for total element analysis of Vertisols, 20 soils were collected across northern New South Wales (NSW), Australia. Comparison of PXRF results were made with conventional standard microwave aqua regia (AR) digestion followed by inductively couple plasma optical emission spectroscopy (ICP-OES) analysis, laboratory X-ray fluorescence (LXRF), and neutron activation analysis (NAA). Strong linear correlations were found for As, Ca, Cr, Cu, Fe, K, Mg, Mn, Ni, P, Pb, Si, Ti, and Zn. We demonstrate that nondestructive analyses for total soil element determination, particularly Ca, Fe, Mn, and P, should now allow rapid elucidation of important chemical processes in Vertisols that are commonly only available following rigorous sample preparation and digestion. The integrated and robust character of PXRF instrumentation, requiring minimal or no dedicated laboratory infrastructure, is readily adaptable to a wide range of analytical situations.

Solution 31P nuclear magnetic resonance (NMR) spectroscopy on sodium hydroxide–ethylenediaminetetraacetic acid (NaOH–EDTA) extracts can provide detailed characterization of soil organic P, but has not been previously applied widely to Vertisols. Vertisol soils were collected at two depths (0–10 cm and 10–30 cm) for chemical and spectroscopic analysis. Sodium hydroxide–EDTA extracted a relatively consistent proportion (17 to 37%; average 25%) of the total organic P content determined by the ignition–H2SO4 extraction technique. Orthophosphate monoesters were the dominant form of organic P detected by solution 31P NMR spectroscopy of the NaOH–EDTA extracts, the majority of which appeared to be present in large ‘humic’ molecules, based on the predominance of a broad peak in the NMR spectra; some smaller signals due to glycerophosphate, inositol phosphates, and RNA‐derived mononucleotides were also evident. The composition of organic P in the topsoil layer was very similar to that in the subsoil layer. Strong correlations were found between soil organic carbon (C) and nitrogen (N) and extractable organic P, which suggests that processes regulating the cycling of organic C and N are closely related to that for organic P in these Vertisols.

Aqueous and solid-state antimony (Sb) and arsenic (As) speciation is assessed in an Australian freshwater system contaminated by mining of primary sulfide minerals. The study aims to understand metalloid transformation and mobilisation in the system, and coincides with a severe drought providing the opportunity to examine the influence of extreme low-flow conditions. X-ray absorption spectra identified only SbV in <2 mm sediments, despite boulder size stibnite evident in the creek. Roméite-group minerals were detected by X-ray diffraction in oxidation rims of creek-bed stibnite, which potentially limit the contribution of dissolved SbIII to the waterway. Arsenic in <2 mm sediments was dominated by AsV (17–91 %) and orpiment (16–93 %), while the co-occurrence of AsIII (11–36 %) with orpiment suggests that primary As minerals are an important ongoing source of AsIII to the system. Dissolved metalloids (<45 µm filtered) dominated total water column concentrations and comprised mainly pentavalent species. Arsenic(III) was however identified in most water samples (up to 6.6 µg L−1), while dissolved SbIII was only detected in one sample (3.4 µg L−1) collected during the drought period. Dissolved AsV increased significantly in samples collected in low-flow conditions, considered a result of reductive dissolution of sediment Fe-oxyhydroxide host phases, but a similar increase in dissolved Sb was not observed. This study highlights a greater risk from As in this system, and the likelihood of increased As mobility under the warmer and drier environmental conditions predicted with climate change, especially during first-flush events.