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Evolution (Terrestrial Plants: CO2-Induced) -- Summary
Some two decades ago, Root and Schneider (1993) wrote that CO2-induced changes in global climate were expected - by them and other climate alarmists - to occur "too fast for evolutionary processes such as natural selection to keep pace," while adding that this phenomenon "could substantially enhance the probability of extinction of numerous species."

This famous but unsubstantiated declaration has ever since pervaded the thinking of the world's climate-alarmists. But is the highly-hyped contention correct? This document broaches that question as it pertains to demonstrable CO2-induced changes in natural (i.e., non-agricultural) terrestrial vegetation, as revealed by a number of subsequent scientific studies.

In introducing the report of their investigation of the subject, Rae et al. (2007) wrote that various studies "are beginning to identify genes that appear sensitive to elevated CO2 (Gupta et al., 2005; Taylor et al., 2005; Ainsworth et al., 2006)," while noting that "leaf growth responses to elevated CO2 have been found in Populus," and that "quantitative trait loci (QTL) for this response [have been] determined (Rae et al., 2006)." And in a continuation of this endeavor, they worked with a three-generation Populus pedigree generated by the hybridization of two contrasting Populus species - where two full-siblings from the resulting F1 family were crossed to form an F2 family - growing cuttings of the different generations for 152 days out-of-doors in open-top chambers maintained at either the ambient CO2 concentration or concentrations on the order of 600 ppm, while measuring various plant properties and physiological processes and determining QTL for above- and below-ground growth and genotype-by-environment interactions.

This work revealed, in the words of the four UK researchers, that "in the F2 generation, both above- and below-ground growth showed a significant increase in elevated CO2," and that "three areas of the genome on linkage groups I, IX and XII were identified as important in determining above-ground growth response to elevated CO2, while an additional three areas of the genome on linkage groups IV, XVI and XIX appeared important in determining root growth response to elevated CO2." Consequently, stating that their results "quantify and identify genetic variation in response to elevated CO2 and provide an insight into genomic response to the changing environment," they concluded that further work in this area "should lead to an understanding of micro-evolutionary response to elevated CO2," as has been further demonstrated to be the case by subsequent studies.

One year later, working within controlled-environment chambers maintained at atmospheric CO2 concentrations of either 380 or 700 ppm, Springer et al. (2008) grew well watered and fertilized plants of two closely related out-crossed genotypes (SG and CG) of Arabidopsis thaliana that had been generated via artificial selection, where genotype SG was selected for high seed number at elevated CO2 over five generations, and where genotype CG was randomly selected and thus represented a non-selected control. For these plants, they measured time to flowering, number of leaves at flowering, and total biomass at flowering, as well as foliar sugar concentrations; and then - in a second experiment conducted under the same growing conditions - they characterized the expression patterns of several floral-initiation genes.

This work revealed, in the words of Springer et al., that "SG delayed flowering by 7-9 days, and flowered at a larger size (122% higher biomass) and higher leaf number (81 more leaves) when grown at elevated versus current CO2 concentration," but that "flowering time, size and leaf number at flowering were similar for CG plants grown at current and elevated CO2." In addition, they found that "SG plants had 84% higher foliar sugar concentrations at the onset of flowering when grown at elevated versus current CO2, whereas foliar sugar concentrations of CG plants grown at elevated CO2 only increased by 38% over plants grown at current CO2." Last of all, they reported that "SG exhibited changes in the expression patterns of floral-initiation genes in response to elevated CO2, whereas CG plants did not."

Noting that "delayed flowering increases production of vegetative resources that can be subsequently allocated to reproductive structures," the researchers concluded that "such evolutionary responses may alter total carbon gain of annual plants if the vegetative stage is extended, and may potentially counteract some of the accelerations in flowering that are occurring in response to increasing temperatures." Hence, their results demonstrated the ability of elevated CO2 to alter the expression of plant genes in ways that may enable plants to take better advantage of the ongoing rise in the air's CO2 content.

Contemporaneously, Lau et al. (2008) measured the amount of pathogen damage caused by Pythium or Fusarium spp. to the common prairie legume Lespedeza capitata growing in ambient and elevated (560 ppm) CO2 treatments in the seventh and eighth full years (2004 and 2005) of the BioCON study (Reich et al., 2001) conducted at the Cedar Creek Natural History Area in Minnesota (USA), where the CO2 treatments were applied during the daylight hours of each growing season. In doing so, they found that disease incidence was lower in the elevated CO2 environment (down by 10% in 2004 and 53% in 2005). And "because disease caused major reductions in reproductive output," in the words of the five researchers, they concluded that "the effects of CO2 on disease incidence may be important for L. capitata evolution and population dynamics," which phenomena should significantly benefit this species in a high-CO2 world of the future. In addition, they indicated that Strengbom and Reich (2006), "working in the same experimental site ... also found that elevated CO2 ... reduced disease incidence on Solidago rigida."

Concluding this category of study, Kaligaric et al. (2008) investigated fluctuating asymmetry (FA), a descriptor of the magnitude of random deviations from perfect symmetry in morphological traits of both plants and animals that "offers a unique tool for comparative studies of developmental stability (Moller and Swaddle, 1997)," which in plants has been used as "an indicator of genetic and environmental stress (Martel et al., 1999; Cornelissen and Stiling, 2004)." This they did by measuring the degree of FA in "undamaged (not grazed, not visibly attacked by herbivores or pathogens) fully developed leaves" of the Mediterranean shrub Myrtus communis growing along an atmospheric CO2 gradient (570, 530, 490, 450, 410 and 370 ppm) moving away from a natural CO2 spring (I Borboi) near Lajatico (Pisa, Tuscany, Italy) at distances of 2, 18, 34, 50, 66 and 82 meters, respectively, from the CO2 source. And what did they learn?

The four researchers said that they found "a significant and negative correlation between CO2 concentration and leaf FA," such that "with increased CO2 concentration the leaf FA decreased," which result, in their words, "confirms what was obtained by Cornelissen et al. (2004) on Quercus myrtifolia and Quercus geminata (in a short-term experiment)." In addition, they said that "Myrtus communis, grown under elevated CO2 concentration at 'I Borboi,' showed a reduction in xylem embolism and an increase in hydraulic efficiency (Tognetti et al., 2001)," stating that "improved water relations could represent a good explanation for the observed reduction in leaf FA" as the air's CO2 content increased. Hence, they concluded that "adaptation and selection could explain the tendency towards decreased leaf FA in plants from the CO2 spring relative to ambient conditions," since "the more symmetrical leaves under long-term elevated CO2 concentration were more developmentally stable in these conditions."

Shortly thereafter, in a paper published in New Phytologist, Onoda et al. (2009) wrote 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 reported 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 hastened 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 avoided 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 called "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 noted that these results suggest "there is substantial room for plant evolution in high-CO2 environments." Further to this point, they said that 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. concluded 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.

Also with a relevant study published about the same time were Cseke et al. (2009), who noted that certain perceived "genetic and environmental bottlenecks" may limit a plant's capacity to allocate assimilated carbon to greater biomass production. However, it is not illogical to expect that numerous species may possess the genetic diversity needed to overcome these potential roadblocks and thereby benefit more than is commonly anticipated from the enhanced growth that is known to be possible in a CO2-enriched atmosphere.

Working at the Aspen FACE site near Rhinelander, Wisconsin (USA) in the pursuit of such anticipated knowledge, Cseke et al. grew two quaking aspen (Populus tremuloides Michx.) clones (216 and 271) from the seedling stage in replicate plots maintained at either 372 or 560 ppm CO2 throughout each year's growing season (May-September), assessing their stem volume (a surrogate for biomass) annually for a period of eight years, during and after which time they measured: (1) the trees' maximum light-saturated rates of leaf net photosynthesis, (2) the transcriptional activity of leaf elevated-CO2-responsive genes, and (3) numerous leaf primary and secondary carbon-based compounds. This work revealed that although the CO2-induced increase in the maximum light-saturated rate of leaf net photosynthesis in clone 216 was over twice as great as that of clone 271 (37% vs. 17%, as best as can be determined from Cseke et al.'s bar graphs), just the opposite relationship was manifest in the CO2-induced increases in the trees' stem volumes (only 0-10% for clone 216 vs. 40-50% for clone 271).

As for why this was so, the researchers' transcript abundance and carbon/nitrogen biochemistry data suggested that "the CO2-responsive clone (271) partitions carbon into pathways associated with active defense/response to stress, carbohydrate/starch biosynthesis and subsequent growth," while "the CO2-unresponsive clone (216) partitions carbon into pathways associated with passive defense and cell wall thickening." Thus, the seven scientists concluded there was "significant variation in expression patterns between different tree genotypes in response to long-term exposure to elevated CO2," and that "future efforts to improve productivity or other advantageous traits for carbon sequestration should include an examination of genetic variability in CO2 responsiveness." And it is also to be noted that as the atmosphere's CO2 concentration continues to rise, manifestations of these fitness-promoting traits will appear on their own, as they are brought forth naturally by the changing environment, seeing that earth's plants appear to be genetically programmed to respond positively to atmospheric CO2 enrichment, which further suggests that the ongoing rise in the air's CO2 concentration is something they are innately well prepared to use to their advantage.

Rounding out this brief review of the subject is the study of Nakamura et al. (2011), who suggested 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 noted 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, in their words, "been exposed to high CO2 over an evolutionary time scale," citing the work of Miglietta et al. (1993) and Raschi et al. (1999).

Nakamura et al. thus 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 and which they presumed to have been typical of CO2 concentrations at those locations over what they called "an evolutionary time scale."

As a result of their efforts in this regard, the six scientists "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 they said "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 therefore concluded that "a higher potential of biomass production contributes to fitness and has selective advantages."

Noting that their results were "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. concluded that their study "clearly shows that phenotypic and genetic differences have occurred between high and normal CO2 populations."

In conclusion, and in light of all of the scientific findings described above, it would appear that the ongoing rise in the air's CO2 content is likely exerting significant selection pressure on earth's naturally-occurring terrestrial plants, which should improve their performance in the face of various environmental stressors via the process of micro-evolution as the atmosphere's CO2 concentration continues to rise in the years and decades ahead.

Ainsworth, E.A., Rogers, A., Vodkin, L.O., Walter, A. and Schurr, U. 2006. The effects of elevated CO2 concentration on soybean gene expression. An analysis of growing and mature leaves. Plant Physiology 142: 135-147.

Collins, S. and Bell, G. 2004. Phenotypic consequences of 1000 generations of selection at elevated CO2 in a green alga. Nature 431: 566-569.

Cornelissen, T. and Stiling, P. 2004. Perfect is best: how leaf fluctuating asymmetry reduces herbivory by leaf miners. Oecologia 142: 46-56.

Cornelissen, T., Stiling, P. and Drake, B. 2004. Elevated CO2 decreases leaf fluctuating asymmetry and herbivory by leaf miners on two oak species. Global Change Biology 10: 27-36.

Cseke, L.J., Tsai, C.-J., Rogers, A., Nelsen, M.P., White, H.L., Karnosky, D.F. and Podila, G.K. 2009. Transcriptomic comparison in the leaves of two aspen genotypes having similar carbon assimilation rates but different partitioning patterns under elevated [CO2]. New Phytologist 182: 891-911.

Fordham, M., Barnes, J.D., Bettarini, I., Polle, A., Slee, N., Raines, C., Miglietta, F. and Raschi, A. 1997. The impact of elevated CO2 on growth and photosynthesis in Agrostis canina L ssp. monteluccii adapted to contrasting atmospheric CO2 concentrations. Oecologia 110: 169-178.

Gupta, P., Duplessis, S., White, H., Karnosky, D.F., Martin, F. and Podila, G.K. 2005. Gene expression patterns of trembling aspen trees following long-term exposure to interacting elevated CO2 and tropospheric O3. New Phytologist 167: 129-142.

Kaligaric, M., Tognetti, R., Janzekovic, F. and Raschi, A. 2008. Leaf fluctuating asymmetry of Myrtus communis L., affected by increases in atmospheric CO2 concentration: Evidence from a natural CO2 spring. Polish Journal of Environmental Studies 17: 503-508.

Kohut, R. 2003. The long-term effects of carbon dioxide on natural systems: issues and research needs. Environment International 29: 171-180.

Lau, J.A., Shaw, R.G., Reich, P.B., Shaw, F.H. and Tiffin, P. 2007. Strong ecological but weak evolutionary effects of elevated CO2 on a recombinant inbred population of Arabidopsis thaliana. New Phytologist 175: 351-362.

Lau, J.A., Strengbom, J., Stone, L.R., Reich, P.B. and Tiffin, P. 2008. Direct and indirect effects of CO2, nitrogen, and community diversity on plant-enemy interactions. Ecology 89: 226-236.

Martel, J., Lempa, K. and Haukioja, E. 1999. Effects of stress and rapid growth on fluctuating asymmetry and insect damage in birch leaves. Oikos 86: 208-216.

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.

Moller, A. and Swaddle, J.P. 1997. Asymmetry, Developmental Stability and Evolution. Oxford University Press, Oxford, UK.

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.

Onoda, Y., Hirose, T. and Hikosaka, K. 2009. Does leaf photosynthesis adapt to CO2-enriched environments? An experiment on plants originating from three natural CO2 springs. New Phytologist 182: 698-709.

Polle, A., McKee, I. and Blaschke, L. 2001. Altered physiological and growth responses to elevated [CO2] in offspring from holm oak (Quercus ilex L.) mother trees with lifetime exposure to naturally elevated [CO2]. Plant, Cell & Environment 24: 1075-1083.

Rae, A.M., Ferris, R., Tallis, M.J. and Taylor, G. 2006. Elucidating genomic regions determining enhanced leaf growth and delayed senescence in elevated CO2. Plant, Cell & Environment 29: 1730-1741.

Rae, A.M., Tricker, P.J., Bunn, S.M. and Taylor, G. 2007. Adaptation of tree growth to elevated CO2: quantitative trait loci for biomass in Populus. New Phytologist 175: 59-69.

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.

Reich, P.B., Tilman, D., Craine, J., Ellsworth, D., Tjoelker, M.G., Knops, J., Wedin, D., Naeem, S., Bahauddin, D., Goth, J., Bengston, W. and Lee, T.D. 2001. Do species and functional groups differ in acquisition and use of C, N, and water under varying atmospheric CO2 and N availability regimes? A field test with 16 grassland species. New Phytologist 150: 435-448.

Root, T.L. and Schneider, S.H. 1993. Can large-scale climatic models be linked with multiscale ecological studies? Conservation Biology 7: 256-270.

Schulte, M., Von Ballmoos, P., Rennenberg, H. and Herschbach, C. 2002. Life-long growth of Quercus ilix L. at natural CO2 springs acclimates sulphur, nitrogen and carbohydrate metabolism of the progeny to elevated pCO2. Plant, Cell & Environment 25: 1715-1727.

Springer, C.J., Orozco, R.A., Kelly, J.K. and Ward, J.K. 2008. Elevated CO2 influences the expression of floral-initiation genes in Arabidopsis thaliana. New Phytologist 178: 63-67.

Strengbom, J. and Reich, P.B. 2006. Elevated CO2 and increased N supply reduce leaf disease and related photosynthetic impacts on Solidago rigida. Oecologia 149: 519-525.

Taylor, G., Street, N.R., Tricker, P.J., Sjodin, A., Graham, L., Skogstrom, O., Calfapietra, C., Scarascia-Mugnozza, G. and Jansson, S. 2005. The transcriptome of Populus in elevated CO2. New Phytologist 167: 143-154.

Thomas, S.C. and Jasienski, M. 1996. Genetic variability and the nature of micro-evolutionary response to elevated CO2. In: Korner, C. and Bazzaz, F.A. (Eds.) Carbon Dioxide, Populations and Communities. Academic Press, Inc., San Diego, California, USA, pp. 51-81.

Tognetti, R., Longobucco, A., Raschi, A. and Jones, M.B. 2001. Stem hydraulic properties and xylem vulnerability to embolism in three co-occurring Mediterranean shrubs at a natural CO2 spring. Australian Journal of Plant Physiology 28: 257-268.

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.

Woodward, F.I., Thompson, G.B. and McKee, I.F. 1991. The effects of elevated concentrations of carbon dioxide on individual plants, populations, communities and ecosystems. Annals of Botany 67: 23-38.

Last updated 5 February 2014