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Evolutionary Responses of a C3 Perennial Herb to Elevated CO2
Nakamura, I., Onoda, Y., Matsushima, N., Yokoyama, J., Kawata, M. and Hikosaka, K. 2011. Phenotypic and genetic differences in a perennial herb across a natural gradient of CO2 concentration. Oecologia 165: 809-818.

The authors write that "evolutionary responses to elevated CO2 in wild plants are, in general, difficult to detect using growth experiments, because the duration of experiments is often too short compared to the time required for evolution." However, they note that areas around natural CO2 springs -- and locations nearby but beyond the influence of the springs on the air's CO2 content -- provide ideal sources of plants for such studies, since the plants in the first of these locations "have been exposed to high CO2 over an evolutionary time scale," citing the work of Miglietta et al. (1993) and Raschi et al. (1999).

What was done
Nakamura et al. conducted several different types of experiments designed to reveal numerous characteristics of Plantago asiatica plants (a C3 rosette perennial herb) acquired from a number of locations at different distances from a stream emerging from a CO2-emitting spring situated at the foot of Mount Gassan (Japan), where the plants had been exposed to normal ambient (370 ppm) and several different elevated (726, 771, 1044 and 5339 ppm) CO2 concentrations, as measured in late August and early September in two different years, which they presumed to have been typical of CO2 concentrations at those locations over "an evolutionary time scale."

What was learned
The six scientists say they "found phenotypic differences between populations in areas with high and normal CO2, some of which were heritable," indicating that "an evolutionary differentiation occurred in the P. asiatica population across a CO2 gradient." One of these differences was in plant relative growth rate, which "was higher in parent plants that originated in areas with higher CO2, suggesting that plants from higher CO2 populations had an inherent potential for higher productivity." And they say it is likely that "a higher potential of biomass production contributes to fitness and has selective advantages."

What it means
Noting that their results "are consistent with those of previous experiments, wherein artificial selection increased seed production under the respective CO2 condition compared to non-selected plants (Ward et al., 2000; Ward and Kelly, 2004)," Nakamura et al. conclude that their study "clearly shows that phenotypic and genetic differences have occurred between high and normal CO2 populations."

Miglietta, F., Raschi, A., Bettarini, I., Resti, R. and Selvi, F. 1993. Natural CO2 springs in Italy: a resource for examining long-term response of vegetation to rising atmospheric CO2 concentrations. Plant, Cell and Environment 16: 873-878.

Raschi, A., Miglietta, F., Tognetti, R. and van Gardingen, P.R. 1999. Plant Responses to Elevated CO2. Evidence from Natural Springs. Cambridge University Press, Cambridge, UK.

Ward, J.K., Antonovics, J., Thomas, R.B. and Strain, B.R. 2000. Is atmospheric CO2 a selective agent on model C3 annuals? Oecologia 123: 330-341.

Ward, J.K. and Kelly, J.K. 2004. Scaling up evolutionary responses to elevated CO2: lessons from Arabidopsis. Ecology Letters 7: 427-440.

Reviewed 13 April 2011