Growth and Yield of CO₂-Enriched Wheat Under Water-Limited Conditions

Abstract

Wheat was grown at a density of 120 plants m^-2 in deep pots of soil in two artificially illuminated growth cabinets. One cabinet was left at ambient CO₂ levels and the other enriched by 250 volumes per million (vpm). Four levels of growth-restricting water supply were imposed. Responses by the two cultivars used (Gabo and WW15) did not differ appreciably in terms of the mature crop dry-weight parameters examined.

Comparison of the crop responses to water supply indicated sufficient correspondence between generalized field behaviour and cabinet behaviour to justify tentative interpretation of the results in terms of possible response of water-limited field wheat crop yields to the globally rising level of atmospheric CO₂.

The less water made available to the crop the less was the absolute response of grain yield to CO₂ enrichment, but the greater was the response relative to the control yield. Under extreme aridity (about 100-120 mm crop transpiration overall), the data implied infinite relative enhancement of yield due to CO₂ enrichment, because it allowed some grain growth where none occurred without extra CO₂. The absolute yield enhancement was equivalent to 5-13 kg ha^-1 per 1.2 vpm increment of atmospheric CO₂ concentration. The level of CO₂ in the global atmosphere is currently rising by about 1.2 vpm year^-1. The higher temperature at which the crops were grown (19°C), relative to average field conditions in many wheat areas, may influence this interpretation.