School of Agriculture, Food and Ecosystem Sciences - Research Publications
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ItemCan additional N fertiliser ameliorate the elevated CO2-induced depression in grain and tissue N concentrations of wheat on a high soil N background?(WILEY, 2017-12)Elevated CO₂ stimulates crop yields but leads to lower tissue and grain nitrogen concentrations [N], raising concerns about grain quality in cereals. To test whether N fertiliser application above optimum growth requirements can alleviate the decline in tissue [N], wheat was grown in a Free Air CO₂ Enrichment facility in a low‐rainfall cropping system on high soil N. Crops were grown with and without addition of 50–60 kg N/ha in 12 growing environments created by supplemental irrigation and two sowing dates over 3 years. Elevated CO₂ increased yield and biomass (on average by 25%) and decreased biomass [N] (3%–9%) and grain [N] (5%). Nitrogen uptake was greater (20%) in crops grown under elevated CO₂. Additional N supply had no effect on yield and biomass, confirming high soil N. Small increases in [N] with N addition were insufficient to offset declines in grain [N] under elevated CO₂. Instead, N application increased the [N] in straw and decreased N harvest index. The results suggest that conventional addition of N does not mitigate grain [N] depression under elevated CO₂, and lend support to hypotheses that link decreases in crop [N] with biochemical limitations rather than N supply.
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ItemWater availability moderates N2 fixation benefit from elevated [CO2]: A 2-year free-air CO2 enrichment study on lentil (Lens culinaris MEDIK.) in a water limited agroecosystem(WILEY, 2018-10)Increased biomass and yield of plants grown under elevated [CO2 ] often corresponds to decreased grain N concentration ([N]), diminishing nutritional quality of crops. Legumes through their symbiotic N2 fixation may be better able to maintain biomass [N] and grain [N] under elevated [CO2 ], provided N2 fixation is stimulated by elevated [CO2 ] in line with growth and yield. In Mediterranean-type agroecosystems, N2 fixation may be impaired by drought, and it is unclear whether elevated [CO2 ] stimulation of N2 fixation can overcome this impact in dry years. To address this question, we grew lentil under two [CO2 ] (ambient ~400 ppm and elevated ~550 ppm) levels in a free-air CO2 enrichment facility over two growing seasons sharply contrasting in rainfall. Elevated [CO2 ] stimulated N2 fixation through greater nodule number (+27%), mass (+18%), and specific fixation activity (+17%), and this stimulation was greater in the high than in the low rainfall/dry season. Elevated [CO2 ] depressed grain [N] (-4%) in the dry season. In contrast, grain [N] increased (+3%) in the high rainfall season under elevated [CO2 ], as a consequence of greater post-flowering N2 fixation. Our results suggest that the benefit for N2 fixation from elevated [CO2 ] is high as long as there is enough soil water to continue N2 fixation during grain filling.
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ItemThe relationship between transpiration and nutrient uptake in wheat changes under elevated atmospheric CO2(WILEY, 2018-08)The impact of elevated [CO2 ] (e[CO2 ]) on crops often includes a decrease in their nutrient concentrations where reduced transpiration-driven mass flow of nutrients has been suggested to play a role. We used two independent approaches, a free-air CO2 enrichment (FACE) experiment in the South Eastern wheat belt of Australia and a simulation study employing the agricultural production systems simulator (APSIM), to show that transpiration (mm) and nutrient uptake (g m-2 ) of nitrogen (N), potassium (K), sulfur (S), calcium (Ca), magnesium (Mg) and manganese (Mn) in wheat are correlated under e[CO2 ], but that nutrient uptake per unit water transpired is higher under e[CO2 ] than under ambient [CO2 ] (a[CO2 ]). This result suggests that transpiration-driven mass flow of nutrients contributes to decreases in nutrient concentrations under e[CO2 ], but cannot solely explain the overall decline.
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ItemA reduced-tillering trait shows small but important yield gains in dryland wheat production(WILEY, 2020-07)Reducing the number of tillers per plant using a tiller inhibition (tin) gene has been considered as an important trait for wheat production in dryland environments. We used a spatial analysis approach with a daily time-step coupled radiation and transpiration efficiency model to simulate the impact of the reduced-tillering trait on wheat yield under different climate change scenarios across Australia's arable land. Our results show a small but consistent yield advantage of the reduced-tillering trait in the most water-limited environments both under current and likely future conditions. Our climate scenarios show that whilst elevated [CO2 ] (e[CO2 ]) alone might limit the area where the reduced-tillering trait is advantageous, the most likely climate scenario of e[CO2 ] combined with increased temperature and reduced rainfall consistently increased the area where restricted tillering has an advantage. Whilst long-term average yield advantages were small (ranged from 31 to 51 kg ha-1 year-1 ), across large dryland areas the value is large (potential cost-benefits ranged from Australian dollar 23 to 60 MIL/year). It seems therefore worthwhile to further explore this reduced-tillering trait in relation to a range of different environments and climates, because its benefits are likely to grow in future dry environments where wheat is grown around the world.