Below-ground processes


Evaluation of the effect of elevated carbon dioxide (eCO2) on plant production must consider the below-ground aspects that determine crop resource use efficiency. Elevated CO2 causes changes in plant chemistry which will in turn change soil properties and processes. At the same time, direct eCO2 effects on plant function will alter root architecture and function. AGFACE, with its integrated SoilFACE facility, provides a unique opportunity to study such complex systems.

Results to date

SoilFACE studies have focused on phosphorus (P), nitrogen (N) and carbon (C) processes. Researchers have shown that although P and N uptake and nodule number in legumes increase at eCO2, the difference is due to increased above- and below-ground biomass production rather than from changes in specific root-absorbing capability or specific nodule function. The increase in N demand (due to greater biomass) is not compensated by greater N use efficiency, meaning more fertiliser-N or legume-N is required to meet crop demand.

Grain protein content in chickpea was reduced at eCO2 but in field pea this depended on soil P levels: eCO2 increased grain P under limited soil P conditions. Thus, the effect of future eCO2 on grain quality will be dependent on both the crop type and agronomic management.

It appears that under eCO2, addition of non-legume crop residue may result in N immobilisation to the subsequent crop, possibly due to concomitant increases in the C:N ratio of crop residues.

Taken together, soil experiments have shown that increased above- and below-ground crop biomass requires more N and P inputs for crops to take advantage of the ‘CO2 fertilisation' effect. Legumes may become important in future cropping systems to supply N to succeeding cereal crops but will only be able to supply this if sufficient P is available for N fixation.

Related resources

Titlesort descending Excerpt
AGFACE fact sheet (2014) Fact sheet profiling the project Australian Grains Free Air Carbon dioxide Enrichment program.
Roger Armstrong - AGFACE and SoilFACE results: Below ground soil:plant processes Presented by Roger Armstrong, DEPI, at the AGFACE Crop Science Workshop.