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Response of a C3 Forb to Elevated Atmospheric CO2 and Nocturnal Air Temperature
Wolfe-Bellin, K.S., He, J.-S. and Bazzaz, F.A. 2006. Leaf-level physiology, biomass, and reproduction of Phytolacca americana under conditions of elevated carbon dioxide and increased nocturnal temperature. International Journal of Plant Science 167:1011-1020.

The authors note that "nocturnal temperatures are predicted to increase more than diurnal temperatures," as has also been observed in the real world over much of the 20th century, and that it might be expected that "increased nocturnal temperature would increase dark respiration rate" and thereby "diminish the positive effects of elevated CO2 on whole-plant growth, as measured by total biomass."

What was done
In an experiment designed to explore this hypothesis, Wolfe-Bellin et al. grew the C3 forb Phytolacca americana L. from the four-leaf stage to maturity under well watered and fertilized conditions in 6.2-L containers filled with a general purpose growing medium within controlled-environment glass chambers maintained at either 370 or 740 ppm CO2 at diurnal/nocturnal temperatures of either 26/20C or 26/24C, during which time they periodically measured their light-saturated photosynthetic rates and whole-plant biomass.

What was learned
The three researchers report that plant "photosynthetic rate was greater under elevated CO2 [+69% during the first part of the growing season], while dark respiration rate, predicted to increase under higher nocturnal temperatures, exhibited no response to the nocturnal temperature treatment." Hence, they say that in contrast to their prediction, the forb they studied "exhibited no diminishment of total plant size in response to elevated nocturnal temperature." In addition, they found that "time to flowering decreased and biomass allocation to reproduction increased under conditions of elevated nocturnal temperatures."

What it means
In the words of Wolfe-Bellin et al., "since elevated CO2 increased total plant biomass and higher nocturnal temperatures increased allocation to reproduction, the results indicate that elevated CO2 and high nocturnal temperatures of the future could have a neutral or even positive effect on the growth of northern P. americana populations," even to the extent of "increasing population sizes, at least for plants growing at the northern edge of the species' range."

Reviewed 28 November 2007