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Effects of Elevated CO2 on Growth Responses of Soybeans to High Temperature and UV-B Radiation
Reference
Koti, S., Reddy, K.R., Kakani, V.G., Zhao, D. and Gao, W. 2007. Effects of carbon dioxide, temperature and ultraviolet-B radiation and their interactions on soybean (Glycine max L.) growth and development. Environmental and Experimental Botany 60: 1-10.

What was done
The authors grew six different genotypes (D 88-5320, D 90-9216, Stalwart III, PI 471938, DG 5630 RR and DP 4933 RR) of soybean (Glycine max L.) from seed to maturity in 2.5-L pots within Soil-Plant-Atmosphere-Research (SPAR) units maintained at two different atmospheric CO2 concentrations - 360 ppm (control) and 720 ppm (+CO2) - under well watered and fertilized conditions, while the plants were exposed to either control day/night temperatures of 30/22C and/or ultraviolet-B radiation of 0 kJ/m2/day or high-stress temperature and UV-B conditions of 38/30C and 10 kJ/m2/day, respectively. Parameters that were measured to evaluate the plants' responses to these treatments were net photosynthesis rate, plant height, leaf area, total biomass, total chlorophyll content, phenolic content, relative injury and wax content.

What was learned
Koti et al. determined that "the +CO2 conditions alone significantly increased total biomass by 21%, averaged over all the genotypes," while "D 88-5320 had the highest positive response (42%)." On the other hand, they found that "plants grown under high temperatures [+T] and enhanced UV-B [+UV-B] radiation had less total biomass, by 18 and 21%, respectively." However, they report that "under +T +CO2 and +UV-B +CO2 conditions, the reductions in biomass were not evident [our italics]." In addition, they say their "results showed that elevated CO2 levels compensated the damaging effects caused by negative stressors such as high temperature and high UV-B radiation levels on most of the growth and physiological parameters studied."

What it means
In harmony with the results of many other studies that have evaluated the negative impacts of these and several other environmental stressors (see Growth Response to CO2 with Other Variables in our Subject Index), the doubling of the air's CO2 content employed by Koti et al. largely compensated for the deleterious effects of the elevated levels of temperature and UV-B radiation they investigated. These findings are good news for man and nature alike.

Reviewed 22 August 2007