Abstract

Global atmospheric carbon-dioxide concentration ([CO₂]) is increasing rapidly, but its interactions with nitrogen (N) and phosphorus (P) fertiliser on wheat grain quality are not well understood. In two experiments, we investigated the effects of ambient [CO₂] (aCO₂; ∼410 ppm) and elevated [CO₂] (eCO₂; 760 ppm) on shoot macro-nutrient content, nutrient harvest index (NuHI) and grain nutrient concentration of wheat supplied low and optimum rates of N and P fertilisers. Elevated [CO₂] increased biomass, grain yield and grain nutrient accumulation in Experiment 1, resulting in reduced grain N, S, Ca and Mg concentration. This was attributed to nutrient ‘dilution’ due to increased carbohydrate content in the grain. In contrast, in Experiment 2, measured variables were unaffected by eCO₂, but grain N, K, Ca and Mg concentrations decreased with increasing [CO₂]. This was attributed to reduced remobilisation of nutrients to the grain during reproductive development at eCO₂. Fertiliser deficiency reduced straw and grain yield by 61–86% across CO₂ treatments and experiments. The element HIs were unaffected by eCO₂, except for MgHI. Our results point to a compensatory and symmetrical interactions between N, P and CO₂ that changes in one element rapidly altering the availability of the other. Furthermore, the results highlight the need for selecting cultivars that are productive and yet maintain suitable quality characteristics under eCO₂.

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