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Elevated CO2 Reduces the Total Water Use of Canola

Paper Reviewed
Uddin, S., Parvin, S., Löw, M., Fitzgerald, G.J., Tausz-Posch, S., Armstrong, R. and Tausz, M. 2019. Water use dynamics of dryland canola (Brassica napus L.) grown on contrasting soils under elevated CO2. Plant and Soil 438: 205-222.

In providing the rationale for their work, Uddin et al. (2019) write that "it is essential to understand the mechanisms underpinning crop responses to future climates to ensure future crop production." And in this regard they note this understanding is particularly important for arid regions where crop yields are limited by water shortage. Thus, it was the goal of this team of seven researchers to investigate the impact of elevated CO2 on the growth and water use efficiency of two canola (Brassica napus) cultivars in a dryland agroecosystem.

The work was carried out at the Australian Grains Free-air CO2 Enrichment (AGFACE) facility in Horsham, Victoria, Australia in the winter season of 2015. Within the FACE apparatus, the two cultivars were grown in large intact soil cores comprised of two different soil types common to the dryland region that were subjected to either ambient (~400 ppm) or elevated (~550 ppm) CO2 during the daylight hours for the length of the growing season.

With respect to their findings, Uddin et al. report that elevated CO2 increased net photosynthesis by 14% and reduced stomatal conductance by 17%, which resulted in a 37% increase in plant water use efficiency. Other positive effect of atmospheric CO2 enrichment included greater plant leaf area, a taller plant, increased siliquae production and a greater number of sound seeds per siliquae. The end result of these many benefits was an average 20% increase in seed yield compared to ambient CO2 grown plants, averaged across both cultivars and soil types.

Uddin et al. also observed the following important finding: "despite greater leaf area, water use in the present study, measured using two different but complementary techniques, was lower under elevated CO2 than ambient CO2." Consequently, there was "no evidence that stimulation of leaf growth offset greater leaf-level water use efficiency, [therefore] water use was decreased [by about 7%] under elevated CO2 under the environmental conditions of the current study." The significance of this latter finding was not lost on the study authors, who thus conclude that "lower water use observed under elevated CO2 may lead to higher water content within the soil profile during the growing season," while adding that "water savings under elevated CO2 may help to overcome a major constraint (susceptibility to drought) limiting the expansion of current Australian canola production." And it will likewise benefit the growth of canola in other arid regions across the globe, and likely other crops grown in those water-limiting regions as well. And that is great news for a crop that "currently ranks second in terms of global importance as a protein source for livestock and third for vegetable oil."

Posted 2 September 2019