Hydrothermal carbonised wastes (hydrochars) can have toxic effects on soil biota, but factors influencing toxin formation in hydrochar and subsequent toxicity to soil organisms have not been elucidated. This study investigated the toxicity of hydrochars on soil biota, with a focus on earthworm (Eisenia fetida) avoidance, microbial metabolic quotient (qCO
Acid soils constrain legume growth and biochars have been shown to address these constraints and enhance biological N2 fixation in glasshouse studies. A dissection of causal mechanisms from multiple crop field studies is lacking. In a sub-tropical field study, faba bean (Vicia faba L.) was cultivated in rotation with corn (Zea mays) following amendment of two contrasting biochars, compost and lime in a rhodic ferralsol. Key soil parameters and plant nutrient uptake were investigated alongside stable 15 N isotope methodologies to elucidate the causal mechanisms for enhanced biological N2 fixation and crop productivity. Biological N2 fixation was associated with plant Mo uptake, which was driven by reductions in soil acidity following lime and papermill (PM) biochar amendment. In contrast, crop yield was associated with plant P and B uptake, and amelioration of soil pH constraints. These were most effectively ameliorated by PM biochar as it addressed both pH constraints and low soil nutrient status. While liming resulted in the highest biological N2 fixation, biochars provided greater benefits to faba bean yield by addressing P nutrition and ameliorating Al toxicity.
Abstract Mineral nutrients in grains act as a source of nutrients in human diets, in which deficiencies of key minerals including calcium, magnesium, copper, iron, and zinc have prompted efforts to increase their concentrations in the edible portions of staple grain crops. Wheat ( Triticum aestivum L.) crops in many regions often suffer abiotic stresses such as drought, extreme heat or frost during grain filling, which affect mineral source–sink relationships. We hypothesized that these stresses would have nutrient‐specific impacts on grain nutrient concentrations due to differences among nutrients in phloem mobility, post‐anthesis uptake and grain loading patterns. Nutrient loading patterns into wheat grains were investigated in two wheat cultivars in the field by sequentially harvesting tagged ears and analyzing tissues for key nutrients. In addition, the impact of perturbed source–sink relations during grain filling on nutrient loading was investigated by inducing post‐anthesis drought /floret abortion in a glasshouse study. Over 90% of Ca and around 70% of Na, K, and Mg accumulated in both wheat cultivars in the field during the first 14 d of grain development. The concentrations of micronutrients (Mn, Fe, Cu and Zn), Mg and P in grains generally increased when florets were aborted, and were unchanged under drought stress, while concentrations of Ca and K were highest under drought stress and lowest under the 66% floret abortion treatment. The observed changes in grain nutrient concentrations from post‐anthesis drought/floret abortion could not be fully explained by nutrient‐specific differences in phloem mobility, post‐anthesis uptake and grain loading patterns. This study will inform future research to define the precise roles of individual nutrients within developing grains and to fully understand the observed variations in grain nutrient concentrations due to source/sink modifications.
Tea tree (Melaleuca alternifolia) is an economically important crop with a narrow natural distribution in eastern Australia. Coastal and upland tea tree ecotypes have been identified based on unique shoot and root traits, but their mycorrhizal associations remain unknown. Dual mycorrhization—the ability of plants to associate with both arbuscular mycorrhizal (AM) and ectomycorrhizal (ECM) fungi—is particularly common among Australian Myrtaceae, including Melaleuca species, but has not yet been investigated in tea tree. We investigated the mycorrhizal associations of tea tree in three coastal and two upland populations using ITS2 metabarcoding and root anatomical observations. Our results revealed that tea tree is a dual mycorrhizal plant, showing variability in root symbioses among ecotypes. ECM percentage root colonisation was significantly lower in the coastal tea tree ecotype compared to the upland ecotype, despite the coastal ecotype exhibiting significantly higher levels of ECM fungal richness. In contrast, the richness of the AM order Glomerales was significantly higher in the coastal tea tree ecotype than in the upland ecotype, yet comparable levels of AM root colonisation were observed between these two ecotypes. Mycorrhizal fungal community composition also differed significantly between coastal and upland ecotypes. Our study provides evidence that tea tree is a dual mycorrhizal species that can host AM and ECM fungi simultaneously within individual plants. Our findings suggest that coastal and upland tea tree ecotypes vary in their associations with mycorrhizal fungi across native habitats, which differ in climate, soil characteristics, and vegetation structure.
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