Tona Sanchez-Palacios

Meteoric-10Be has become a popular proxy for assessing glacial environments and processes around Antarctica, such as meltwater discharge or ice shelf environments. Despite applications in recent paleostudies, little testing of the mechanisms driving the deposition of Be-isotopes into marine sediments has been conducted. We used chemical leach procedures to sequentially or partially extract 10Be and 9Be from bulk sediments to assess the possible sources and depositional processes affecting them. Additionally, we leached the reactive phase of five different grainsize splits to determine whether 10Be/9Be ratios normalise for grainsize effects acting upon the 10Be concentration. Reactive Be-isotopes are primarily situated in the oxide phases of sediments, with the amorphous oxide (Am-Ox) phases consisting of much higher 10Be/9Be ratios (~7–10 × 10−8) than the crystalline oxides (~1–3 × 10−8; X-Ox), indicating that the Am-Ox phase better represents authigenic oxide production and a circumpolar deep water source, which is contrary to most of the current literature. Published leach procedures targeting the reactive phase of sediment consist of ratios in between the Am-Ox and X-Ox phases (~3–7 × 10−8), indicating that they target both phases to some degree. The fractionation of Be-isotopes in Antarctic sediment samples shows that circumpolar deep water is the primary source of 10Be, and that the “reactive” signatures from different leach steps targeting the reactive phase are not the same.

Humans require over 50 essential elements and molecules in their diet including 17 micronutrients, only 8 of which are also essential for plants (chlorine, iron (Fe), manganese (Mn), zinc (Zn), boron (B), copper (Cu), molybdenum Mo), nickel (Ni)). Historically, micronutrients have received less attention in agriculture than N, P and K but their significance has gained prominence through increasing recognition that low levels in staple foods is a major factor in dietary deficiencies for billions of the world’s population, particularly for Fe, Zn, iodine (I) and selenium (Se).

Studies on micronutrients in agriculture emphasise soil and foliar applications for maximising yield rather than their impacts on grain nutrient content. Differences among crop species and cultivars in their ability to mobilise micronutrients in soil explain their varied adaptation to low micronutrient soils. Variations in internal efficiency also exist but most micronutrients have variable phloem mobility which can be a constraint to loading into grain and foods.

For instance, micronutrients in a large collection of grain of an Australian high-yielding wheat cultivar ranged from 21.3 to 97.2 mg Fe/kg grain, 6.9 to 44.7 mg Zn/kg grain, 5 to 25 μg I/kg grain and 3.8 to 829 mg Se/kg grain. For Fe, Zn, Cu, Mo and B, phloem mobility is variable depending on supply, plant N status, plant part, and plant species. Advances in molecular biology are identifying transporters and channels that regulate uptake, distribution and redistribution of micronutrients within plants, especially to grain.

Among wheat genotypes, there are enormous variations in the capacity of plants to extract micronutrients from the soil so that plant breeding has been identified as a key strategy for biofortification of micronutrients in grain. However, efficiencies in uptake don’t necessarily lead to increases in loading of micronutrients in grain. While foliar applications of micronutrients have been effective and accepted as an important strategy for boosting crop yield on low micronutrient soils, there is increasing evidence that efficiency of cellular uptake and retranslocation of common micronutrient salts and chelates is poor.

There is an opportunity to develop enhanced carriers and transporters of micronutrients. New products with enhanced mobility within the plants may also have a role in boosting root growth, particularly in subsoils that are low in Fe, Mn, Cu, Zn and B.

Another potential spin-off from biofortification of micronutrients in grain is increased seed vigour for crop establishment.

Agronomic interventions such as foliar application of fertilisers can increase the mineral content of grains, consequently improving wheat flour for human consumption. We established a field trial at Wongan Hills in Western Australia's moderate rainfall zone (325-450 mm) during the winter season of 2021. Wongan Hills' soil is deficient in available Zn in subsoil layers containing 0.2 ± 0.1 mg Zn-DTPA kg-1.

The topsoil layer, a pale-yellow sandy clay, is Zn adequate with 0.84 ± 0.2 mg Zn-DTPA kg-1. First, we evaluated the efficiency of Zn foliar applications on wheat plants in producing Zn-enriched grains. Second, we used synchrotron radiation techniques to determine the localisation of Zn in grains. Third, we conducted grain quality studies to determine levels of mineral nutrition adequacy in food products. In the field, we tested two Zn forms including ZnSO4 and Zn-EDTA, with or without soluble nitrogen (0.4% N) in the formulation.
Foliar treatments were applied four times from anthesis to grain-filling developmental stages. Foliar-control treatments with and without N produced wheat grains with 13.6 ± 0.4 mg Zn kg-1 and 12.9 ± 0.8 mg Zn kg-1, respectively. Foliar ZnSO4 with and without N resulted in a 2.1- and 1.7-fold increase in Zn concentration relative to controls.

Foliar Zn-EDTA with and without N resulted in a moderate 0.6- and 0.4-fold Zn increase relative to controls. Nitrogen in the formulation did not affect significantly grain yield or concentrations of Zn, iron and phosphorous in grains. X-ray fluorescence microscopy (XFM) studies revealed that Zn was accumulated in the embryo primarily, followed by aleurone layers and to a lesser extent in the crease region in control grains.

Grains of treated plants with Zn foliar fertilisers showed the same distribution pattern with a slight enrichment of Zn in the crease region. Flour milling and bread-making studies showed that Zn-enriched grains derived from ZnSO4 treatment retained twice as much Zn in white bread products with 9.1 ± 0.1 mg Zn kg-1 Zn compared to the control white bread with 3.9 mg Zn kg-1. A moderate increase of Zn relative to controls was observed in white bread produced from the Zn-EDTA foliar treatment at 5.7 ± 0.4 mg Zn kg-1. Similarly, raw noodles from grains of the ZnSO4 treatment retained 6.5 ± 0.1 mg Zn kg-1 which is higher than the control with 2.4 ± 0.05 mg Zn kg-1.

Zinc concentrations in cooked noodles decreased compared to uncooked noodles but still the cooked noodles from flour of Zn enriched grains remained higher with 3.2 mg Zn kg-1 compared to the control at 1.5 mg Zn kg-1.

In conclusion, applying Zn via foliar sprays on wheat resulted in enhanced grain products with dietary Zn advantage, making foliar biofortification a worthwhile agronomic method for agricultural systems with low Zn availability.

Globally, zinc (Zn) deficiency in soils, and subsequently crops, has emerged as one of the most prevalent among micronutrients, resulting in a severe decline in crop yields and nutritional quality and in adversely affecting animal and human health. Worldwide, more than half of the agricultural soils are inherently deficient in Zn, and the health of about one-third of the global human population is impacted by Zn deficiency. Zinc is an essential micronutrient for animal and human health, and, in the developing world, Zn deficiency has been identified as the fifth cause of disease and death for humans. The World Health Organization (WHO) reports that annually more than 800,000 people, including around 450,000 children under the age of 5, die due to Zn deficiency. Zinc supplementation was frequently associated with boosting immunity against COVID-19 in recent years. Because most of the Zn in animals and humans is derived from soil-grown crops, their source of Zn is highly dependent on plant Zn, especially in crops or fodder; in turn, crop Zn is dependent on available soil Zn levels. This integrated review describes Zn distribution, behavior, and fate in soils and its uptake and role in plants and crop production, as well as in the well-being of animals and humans. It discusses recent findings concerning Zn deficiency in all steps of the human food chain (from soil, to crop, animal, and human), and how it can be addressed through novel Zn fertilizers, soil amendments, and biofortification of Zn.

Iodine is an essential micronutrient for human nutrition, though it is found in relatively low concentrations in many important crop species. Wheat (Triticum aestivum L.) is a common staple crop worldwide, and as such could be an important source of dietary iodine due to its widespread consumption. However, little is known about iodine concentrations in wheat grain grown under rainfed field conditions, nor the impact of growing region or environment on these concentrations. Therefore, this paper had three objectives; (1) quantify the iodine concentration in a popular variety of wheat cultivated across the wheat belt of three Australian States (Western Australia, South Australia and Victoria) over two winter seasons (2) determine the influence of distance from the coast, rainfall, elevation, soil type and pH and grain yield on wheat grain iodine concentrations and (3) identify geographical areas where iodine concentrations of wheat grains are low enough that biofortification with iodine would be advantageous for human health outcomes. We sampled iodine concentrations of a single cv. Scepter at 125 sites from the winter season 2020 (65 sites) and 2021(60 sites), to investigate environmental and geographical effects on wheat grain iodine concentrations. Iodine concentrations were measured using triple quadrupole inductively coupled plasma mass spectrometer (ICP MS/MS). We found that the elevation and the region (State) of growing sites were the most significant predictors of iodine concentration, along with the interaction between rainfall and topsoil texture. However, very low concentrations of iodine (5–24 μg/kg) were detected in all samples tested, indicating that even wheat grown under advantageous environmental and geographic conditions in southern Australia would be unlikely to represent an important source of dietary iodine. This emphasises the need to consider biofortification strategies to improve iodine concentrations in Australian grown wheat to improve the dietary uptake of this essential micronutrient by human consumers.

All tables are included in a single .xlsx file across three sheets. Each sheet includes sample information data: expedition and sample location information, reference to corresponding method section in text, and a reference to the source of the method employed for different procedures, or the reference to source data. Footnotes are used where necessary to explain a component of a table.

Supplementary Table 1: All beryllium data used for Sequential, Grainsize, Partial, and Total experiments described in text. 10Be concentration and corresponding 1-sigma (10^8 at/g), 9Be concentration and corresponding 1-sigma (10^15 at/g), and the 10Be/9Be ratio and corresponding 1-sigma (10^-8 at/at).

Supplementary Table 2: Element concentrations (µg/g) from samples across open marine and sub-ice shelf environments and their resultant enrichment factors (EF). Enrichment factors calculated using in text Equation 1. Estimated crustal abundance and ratio displayed below the data table.

Supplementary Table 3: Grainsize of samples used in this study.

Beryllium-10 (10Be) has been proposed as a potential proxy for investigating ice shelf presence and absence, or meltwater discharge in coastal polar environments. However, the sources and distribution of atmospherically produced meteoric-10Be in the Antarctic marine realm are yet to be fully characterized, making any inferences about its concentration in sediments challenging. We present a dataset of 9Be and 10Be concentrations, and 10Be/9Be ratios in seafloor surface sediments from the Antarctic continental shelf - including from sub ice shelf cores - to assess the sources and processes contributing Be-isotopes to ice-sheet proximal marine settings. We show that upwelling waters (e.g. Circumpolar Deep Water) are a significant source of 10Be to continental shelf sediments. This limits the use of 10Be/9Be as a proxy for ice shelf environment or meltwater discharge, but instead provides a potential proxy for reconstructing Circumpolar Deep Water incursions onto Antarctic continental shelves.