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Interactive Effects of Elevated CO2, Excessive Warmth and Water Stress on Photosynthesis and Growth of Canola
Reference
Qaderi, M.M., Kurepin, L.V. and Reid, D.M. 2006. Growth and physiological responses of canola (Brassica napus) to three components of global climate change: temperature, carbon dioxide and drought. Physiologia Plantarum 128: 710-721.

What was done
The authors grew well-fertilized seven-day-old plants for an additional eleven days in controlled-environment chambers maintained at either ambient (370 ppm) or elevated (740 ppm) atmospheric CO2 concentrations in a 2:1:1:0.25 mix of peat moss, Perlite, Vermiculite and Terragreen that was either well-watered (to field capacity) or drought-stressed (at the wilting point) at either low temperatures (22C day / 18C night, which are optimal for canola growth under environmental conditions experienced at Calgary, Canada) or higher more stressful temperatures (28C day / 24C night) while measuring a number of plant physiological parameters and properties, after which they determined the final dry weights of the plants' primary organs.

What was learned
Qaderi et al. report that "drought-stressed plants grown under higher temperature at ambient CO2 had decreased stem height and diameter, leaf number and area, dry matter, leaf area ratio, shoot/root weight ratio, net CO2 assimilation and chlorophyll fluorescence" compared to well-watered plants grown at optimum temperatures in ambient-CO2 air, but that "elevated CO2 generally had the opposite effect, and partially reversed the inhibitory effects of higher temperature and drought on leaf dry weight accumulation." More specifically, and in terms of whole-plant biomass, in the drought-stressed plants grown at higher temperatures in ambient-CO2 air, final dry matter accumulation was reduced by approximately 70% compared to that of the well-watered plants grown at optimum temperatures at the ambient CO2 concentration (as best we can determine from Qaderi et al.'s graphical representations of their results); but when the drought-stressed plants were grown at higher temperatures in elevated-CO2 air, final dry matter accumulation was reduced by a much less drastic 25%, which is quite a feat, considering the soil moisture content of the drought-stressed plants was continuously maintained at the wilting point for one of the worst-case scenarios of CO2-induced warming ever imagined.

What it means
The power of atmospheric CO2 enrichment to reverse the plant-growth-impeding consequences of horrendous drought stress and outlandish increases in temperature is truly amazing. It should be able to more than compensate for the deleterious effects of whatever amount of real-world warming the ongoing rise in the air's CO2 content might possibly produce.

Reviewed 26 January 2011