N dynamics under elevated carbon dioxide in the Australian FACE experiment.

N dynamics under elevated carbon dioxide in the Australian FACE experiment.

Robert M Norton^1,2, S K Lam^2,3, D Chen³, G Fitzgerald⁴, R Armstrong^4
1 International Plant Nutrition Institute, 54 Florence St, Horsham, Victoria, Australia.
Email: rnorton@ipni.net
² Department of Agriculture and Food Systems, The University of Melbourne, Private Box 260, Horsham, Victoria 3401, Australia.
³ Department of Resource Management and Geography, The University of Melbourne, Victoria, 3010, Australia.
⁴ Victorian Department of Primary Industries, Private Bag 260, Horsham, Victoria, 3401, Australia.

Abstract

The Australian Grains Free Air Carbon Dioxide Enrichment (AGFACE) facility was established to compare wheat growth, yield and development under ambient (~380 mol/mol) and elevated (~550 mol/mol) carbon dioxide (a[CO₂] and e[CO₂]). Experiments on N uptake and fertilizer N recovery have been undertaken to estimate how e[CO₂] and a changing climate could affect N supply and demand for annual crop production systems.

When grown under e[CO₂], wheat crops showed higher crop biomass at the end of tillering, anthesis and maturity. Although plant and grain N contents declined, crop N uptake was higher in all three years with e[CO₂]. Root samples taken at anthesis showed that in two of three years, root length density was higher for crops grown under e[CO₂]. Both root biomass and root length density at anthesis also increased in two of the three years of the experiment, although there was no consistent relationship between root length density and N uptake.

Wheat was grown with ¹⁵N enriched urea in PVC microplots in the AGFACE facility. Harvest biomass increased by 23% and N uptake increased by 17% under e[CO₂]. Elevated [CO₂] had no significant effect on the proportion of N derived from fertilizer (%Ndff) for grain, stem and root. There were no significant effects of e[CO₂] on ¹⁵N recoveries in soil and total fertilizer N losses.

These data indicate that e[CO₂] increases growth and plant N demand but there does not seem to be a consistent relationship between N uptake and root density. Wheat under high [CO₂] showed no increase in uptake efficiency from fertilizers or from the soil. Given those two factors, it would appear that the added growth and yield which is a consequence of better C supply will need to be balanced with extra N either from fertilizer or biological sources in future cropping systems.
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