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Pokeweed Responses to Elevated Air Temperature and CO2 Concentration
Kim, Y.O., Rodriguez, R.J., Lee, E.J. and Redman, R.S. 2008. Phytolacca americana from contaminated and noncontaminated soils of South Korea: Effects of elevated temperature, CO2 and simulated acid rain on plant growth response. Journal of Chemical Ecology 34: 1501-1509.

The authors write that in 1979 American pokeweed (Phytolacca americana) "was introduced into South Korea and became an important ecological problem by 1993 when it had spread throughout the country, displacing many native species (Park, 1995)."

What was done
In a greenhouse study, Kim et al. grew P. americana plants from seed they had collected from industrially-contaminated soils (Ulsan, Kyunnam Province) and non-contaminated soils (Suwon, Kyunggi Province). Plants were grown at air temperatures of either 25 or 30C, and at atmospheric CO2 concentrations of either 360 or 650 ppm.

What was learned
Increasing air temperature from 25 to 30C, with no change in the atmosphere's CO2 concentration, was a "mixed bag." It tended to slightly enhance weed growth (as represented by plant length) by 14% in plants grown in non-contaminated soil, while it reduced growth by 27% in weeds grown in contaminated soil, as best we can determine from the bar graphs the researchers present. Increasing the air's CO2 content from 360 to 650 ppm with no change in temperature, on the other hand, was extremely detrimental to weed growth, decreasing it by 44% for plants growing in non-contaminated soil and by 53% for plants growing in contaminated soil. And when both air temperature and CO2 concentration rose together, the net effect was a sizable decline in the growth of weeds growing in both the contaminated soil (26%) and the non-contaminated soil (46%), as the growth-reducing effect of elevated CO2 prevailed.

What it means
In this most interesting study, the effect of enriching the air with CO2 was just the opposite of what it typically is in the case of non-weedy plants: it hurt the weeds rather than helped them.

Park, S.H. 1995. Unrecorded naturalized species in Korea. Korean Journal of Species Taxonomy 25: 123-130.

Reviewed 14 January 2009