Tona Sanchez-Palacios

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.

The successful establishment of vegetation on mine waste tailings relies on the ability of the substrate to sustain plant growth. The phytocap defined as the surface cover system of plants and substrate can convert impacted non-arable mined land into fertile land suitable for cultivation while additionally stabilising tailings. The aim of this study was to investigate the potential to cultivate a fast-growing crop such as industrial hemp (Cannabis sativa L.) as a model plant for phytocapping of mineral waste tailings amended with mixed waste organic outputs (MWOO) from the suburbs of South Sydney, as the capping layer. Chemical characterisation of MWOO revealed high levels of heavy metals including Zn and Pb. Control studies using rhizo lysimeters in the glasshouse showed the potential to cultivate industrial hemp plants in MWOO. Regardless of the content of heavy metals in MWOO, industrial hemp plants showed no symptoms of metal toxicity or deficiency. Determination of total chlorophyll and leaf transpiration confirmed the ability of industrial hemp plants to tolerate high levels of metals in MWOO. Relative stem height growth and total biomass production were used as indicators of performance and showed that MWOO provided the nutrition requirements to cultivate a fast-growing crop such as industrial hemp. Root growth analysis in rhizo lysimeters showed the ability of hemp roots to physically stabilise the MWOO. Determination of soil moisture analysis in rhizo lysimeters showed an increase in evapotranspiration rate with plant development. Further studies will include determination of metals in leachates and below and above ground parts of hemp plants.

Theme: T-5: Advances in sample preparation Type of presentation: Poster-Plus Presentation Application of meteoric-¹ Be (M¹ Be) in sediments and soils from diverse geomorphic settings has been active for many decades. In some cases, M¹ Be is normalized by the reactive Be from the same sediment sample. Given the complexities in geochemical pathways that M¹ Be is incorporated in the reactive mineral phase of such sediments, very different Be isotope chemistry extraction techniques have been developed. Measurement of M¹ Be and the reactive phase of Be in coastal Antarctic marine sediments has increasingly become promising as a paleo-proxy for the presence (or absence) of past ice shelves, and/or sub-glacial meltwater discharge from grounded outlet glaciers draining the ice sheet. However, published works select different methods to chemically leach Be isotopes from the reactive phase of Antarctic marine sediment and few studies have quantitively compared the efficacy of different leaching recipes. This is problematic because comparisons of ¹ Be/ Be ratios across different Antarctic sites assumes the same chemical fractionation of Be isotopes regardless of the leaching method. We examined three large-volume sediment grabs from near the Amery Ice Shelf front in East Antarctica that represent a range of grainsize and environmental conditions. For Be extraction, homogenised materials from each of the three samples were treated with four different leaching procedures, 1 3 targeting the reactive phase: 1) 6M HCl; 2) 0.5M HCl followed by 1M hydroxylamine hydrochloride in 1M HCl; 3) 0.04M hydroxylamine hydrochloride in 25% acetic acid solution 4) a total extraction dissolving in HF, HNO , and HClO. We also selected one grab to assess the effect of grainsize within the following fractions: <38 um, 38 63 um, 63 90 um, 90 125 um, and >125 um. Each fraction was leached with 6M HCl for 24 hours at room temperature. We found that both the 6M HCl and the 1M hydroxylamine procedures leached the same amount of ¹ Be as the total extraction, while the 0.04M hydroxylamine treatment leached only two thirds. Interestingly, the 6M HCl and the 0.04M hydroxylamine procedures leached the same relative proportion of Be to ¹ Be, and thus gave the same ¹ Be/ Be ratio, while the 1M hydroxylamine procedure leached relatively more Be in relation to ¹ Be, resulting in a lower ¹ Be/ Be than the other two methods. As shown in previous studies, our results indicate that Be-isotope concentrations varied inversely with grainsize, in our case increasing 4-fold from coarsest to finest fractions, critically showing that the ¹ Be/ Be ratio remained constant across all grainsizes. Hence, grainsize can be normalised by applying the reactive ¹ Be/ Be ratio. We conclude that differences in leaching procedures, can lead to significant variations in efficiencies in extracting Be isotopes from the reactive phase of sediment, whereas the ¹ Be/ Be ratio appears to remain the same. This study highlights the importance of careful method selection and its consistent application to allow for comparison between studies and more robust interpretation.

An experimental tailings research facility was constructed to allow long-term trials to be conducted in order to investigate the performance and variation in growth and arsenic foliar content in 16 taxa of eucalypts comprising five Eucalyptus spp. with various provenances. A 30 cm deep cover of slurried oxide waste residue was poured on to consolidated arsenic-rich sulphidic gold tailings and was capped with a 10 cm layer of local topsoil. The Eucalyptus were planted in September 2008. The study reported here focusses on the growth responses of candidate Eucalyptus species and provenances in relation to substrate variables (cover depth and arsenic mobility). Three provenances of Eucalyptus cladocalyx grew the fastest and, on average, produced the largest stem volumes. The local provenance of E. goniocalyx was the poorest. Among the other species, Corymbia maculata with provenances from New South Wales and Western Australia (WA) ranked second, E. camaldulensis with provenances from Victoria, WA and South Australia ranked third, and E. tricarpa ranked after these. Owing to its ability to grow under arsenic-rich conditions, more detailed testing of E. cladocalyx involving long-term monitoring of growth, biomass partitioning and foliar arsenic content is required to improve the selection of suitable species and provenances for use in arsenical mineral waste rehabilitation.