In a study of plants from ten different populations of the perennial grass Agrostis curtisii that grows throughout Europe, Norton et al. (1999) could detect no differences in their responses to atmospheric CO2 enrichment. Likewise, Luscher et al. (1998), who collected 9 to 14 genotypes for each of twelve native grassland species growing in Switzerland, could detect no significant differences in CO2 responsiveness within the genotypes of any of the twelve species studied. Similarly, Roumet et al. (2002) grew 14 genotypes of Bromus erectus and Dactylis glomerata at twice-ambient atmospheric CO2 concentrations and found no significant CO2 x genotype interactions. Neither could Midgley et al. (1999) detect any differences in the responses of South African Leucadendron genotypes to atmospheric CO2 enrichment, nor could Klus et al. (2001) for 17 genetic families of Plantago lanceolata.
Studies of several genotypes of quaking aspen have also failed to reveal genotypic differences in growth response to atmospheric CO2 enrichment (Kubiske et al., 1998; King et al., 1999; Zak et al., 2000), as have studies of beech and Norway spruce by Egli et al. (1998) and ponderosa pine by Houpis et al. (1999). All of these studies - as well as experiments with wild radish (Case et al., 1998), mango trees (Schaffer et al., 1977) and honey mesquite (Polley et al., 1999) - thus suggest that the ongoing rise in the air's CO2 content will not become a selective factor that favors one genotype over another. Consequently, if the air's CO2 content continues to rise as it has in the past, it likely will not adversely impact the genotypic diversity of most of earth's plants.
References
Case, A.L., Curtis, P.S. and Snow, A.A. 1998. Heritable variation in stomatal responses to elevated CO2 in wild radish, Raphanus raphanistrum (Brassicaceae). American Journal of Botany 85: 253-258.
Egli, P., Maurer, S., Gunthardt-Goerg, M.S. and Korner, C. 1998. Effects of elevated CO2 and soil quality on leaf gas exchange and aboveground growth in beech-spruce model ecosystems. New Phytologist 140: 185-196.
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Luscher, A., Hendrey, G.R. and Nosberger, J. 1998. Long-term responsiveness to free air CO2 enrichment of functional types, species and genotypes of plants from fertile permanent grassland. Oecologia 113: 37-45.
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