Volume 12, Number 32: 12 August 2009
In a paper recently published in New Phytologist, Onoda et al. (2009) write that the ongoing rise in the air's CO2 content "is likely to act as a selective agent" among earth's plants, citing the studies of Woodward et al. (1991), Thomas and Jasienski (1996), Ward et al. (2000), Kohut (2003), Ward and Kelly (2004) and Lau et al. (2007); and, in fact, they report that "evolutionary responses have been found in selection experiments with short-lived organisms, such as Arabidopsis thaliana (e.g. development rate and biomass production; Ward et al., 2000) and Chlamydomonas reinhardtii (e.g. photosynthesis and cell size; Collins and Bell, 2004)." They hasten to add, however, that "the evolutionary response of wild plants (especially long-lived plants) is, in general, difficult to evaluate using growth experiments," because of the long time spans that are needed to properly evaluate the phenomenon; but they avoid this problem in their newest study by utilizing plants growing around natural CO2 springs, where they "have been exposed to a CO2-enriched atmosphere over many generations," which provides what they call "a unique opportunity to explore the micro-evolutionary response of wild plants to elevated CO2."
In their newest study, therefore, in the words of the three researchers, "the adaptation of leaf photosynthesis to elevated CO2 was tested by a common garden experiment with herbaceous species originating from three different natural CO2 springs in Japan: Nibu, Ryuzin-numa and Yuno-kawa," where "several genotypes were collected from each high-CO2 area (spring population) and nearby control areas (control population), and each genotype was propagated or divided into two ramets, and grown in pots at 370 and 700 ppm CO2," while assessments were made of their photosynthetic nitrogen use efficiency (PNUE), their water use efficiency (WUE), and the degree of carbohydrate accumulation in the plants' leaves, which if too large can lead to the down-regulation of photosynthesis.
In pursuing this protocol, Onoda et al. found that "high CO2 concentration directly and greatly increased PNUE and WUE, suggesting that plants [of the future] will show higher growth rates at a given resource availability." They also found there was "a significant reduction in stomatal conductance, which contributed to higher WUE, and a trend of reduced down-regulation of photosynthesis with a lower starch accumulation," and they note that these results suggest "there is substantial room for plant evolution in high-CO2 environments." Further to this point, they say a still-to-be-published molecular study "also found relatively large genetic differentiation across the CO2 gradient in these plants." Consequently, as a result of their own work and "the increasing number of studies on CO2 springs (e.g. Fordham et al., 1997; Polle et al., 2001; Schlute et al. 2002) and selection experiments (Ward et al., 2000; Collins and Bell, 2004)," Onoda et al. conclude that "high CO2 will act as a selection agent" as the air's CO2 content continues to rise; and this phenomenon should enable earth's plants to fare even better in the CO2-enriched air of the future than they do currently.
Sherwood, Keith and Craig Idso
References
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