CO₂ enrichment and carbon partitioning to phenolics: do plant responses accord better with the protein competition or the growth differentiation balance models?

Abstract

2005. CO 2 enrichment and carbon partitioning to phenolics: do plant responses accord better with the protein competition or the growth-differentiation balance models? Á/ Oikos 111: 337 Á/347.Rising levels of atmospheric CO 2 can alter plant growth and partitioning to secondary metabolites. The protein competition model (PCM) and the extended growth/differentiation balance model (GDB e ) are similar but alternative models that address ontogenetic and environmental effects on whole-plant carbon partitioning to the phenylpropanoid biosynthetic pathway, making many divergent predictions. To test the validity of the models, we compare plant responses to one key prediction: if CO 2 enrichment simultaneously stimulates both photosynthesis and growth, then PCM predicts that partitioning to phenolic compounds will decline, whereas GDB e generally predicts the opposite. Elevated CO 2 (at 548 ppm) increased the biomass growth (ca 23%) as well as the net photosynthesis (ca 13%) of 1-year-old potted paper birch, Betula papyrifera Marsh., in a free air carbon dioxide enrichment study (FACE) in northern Wisconsin. Concomitantly, elevated CO 2 increased carbon partitioning to all measured classes of phenolics (Folin-Denis phenolics, HPLC low molecular weight phenolics (i.e. cinnamic acid derivatives, flavonol glycosides, and flavon-3-ols), condensed tannins, and acid-detergent lignin) in leaves. In stem tissues, tannins and lignin increased, but F-D phenolics did not. In root tissues, F-D phenolics, and tannins increased, but lignin did not. The data suggest that CO 2 enrichment stimulated pathway-wide increase in carbon partitioning to phenylpropanoids. High CO 2 plants had 11.8% more F-D phenolics, 19.3% more tannin, and 10% more lignin than ambient plants after adjusting for plant mass via analysis of covariance. In general, the results unequivocally support the predictions of the GDB e model. By way of contrast, results from many parallel studies on FACE trembling aspen, Populus tremuloides Michx., suggest that although CO 2 enrichment has consistently stimulated both photosynthesis and growth, it apparently did not generally stimulate pathway-wide increases, or decreases, in carbon partitioning to phenylpropanoids in leaves and wood, but rather has specifically, though not consistently, increased partitioning to foliar phenolic glycosides. Likewise, in this case, GDB e 's predictions better accord with the FACE aspen data than PCM's. If further tests of the two models also support GDB rather than PCM, then PCM's main assumption (whole-plant N rather than C is limiting partitioning to phenolic synthesis) may be incorrect.

Do Elevated Temperature and CO2 Generally Have Counteracting Effects on Phenolic Phytochemistry of Boreal Trees?

“…Although the effects of elevated atmospheric CO 2 on plant physiological processes has long been studied, the combined effects of elevated temperature and CO 2 are only poorly known. The growth-differentiation balance model of plant development suggests elevated CO 2 may generally increase carbon partitioning to secondary metabolites like phenyl propanoids because it typically increases plant source strength (rates of photosynthate accumulation) more than sink strength (Herms and Mattson, 1992;Mattson et al, 2005). However, the effects of elevated temperature are much less predictable because it is not fully obvious how that will simultaneously influence both source and sink processes and thus the crucial source-sink carbon balance over plant development.…”

Ecophysiological Responses of Northern Birch Forests to the Changing Atmospheric CO2 and O3 Concentrations

“…With some exceptions, Koike et al (2006) and Wang et al (2009) found a greater amount of tannin in leaves and an increased C/N ratio with CO 2 enrichment; also, herbivorous insects fed with leaves from a high CO 2 environment did less well. Other studies have also found changes in foliar chemical composition due to CO 2 enrichment (Ji et al, 2011;Mattson et al, 2005;Kuokkanen et al, 2003;McDonald et al, 1999). Because herbivory is an important component in C balance of trees, interactions between insect-herbivore and trees should also be taken into account in considering the effect on trees of atmospheric changes (Fig.…”

“…In a high CO 2 environment, the leaf N concentration ordinarily decreases (Zhang et al, 2008;Cao et al, 2007;Mattson et al, 2005;Juurola, 2003;Kuokkanen et al, 2003;McDonald et al, 1999;Tjoelker et al, 1998;Kubiske and Pregitzer, 1996). The reduction in leaf N is partly explained by dilution of leaf N with more assimilates from photosynthesis under elevated CO 2 , consistent with increased starch accumulation (Zhang et al, 2008;Mattson et al, 2005;Rey and Jarvis, 1998;Tjoelker et al, 1998), which is believed to be a factor in the down-regulation of photosynthesis (Peterson et al, 1999;Rey and Jarvis, 1998). The C/N ratio (i.e.…”

“…the ratio of C to N amount in plant tissue) is known to be a good indicator of leaf chemical characteristics. According to the results mentioned above, it is reasonable to suppose that the leaf C/N ratio increases with increasing CO 2 concentration (Koike et al, 2006;Mattson et al, 2005;Juurola, 2003). The increase in the C/N ratio brings changes in the photosynthetic capacity and also in defense capability against herbivores such as insects, which employs phenolic compounds accumulated in leaves.…”

In Defense of Roots: A Research Agenda for Studying Plant Resistance to Belowground Herbivory

“…Nonetheless, differential allocation apparently depends on plant family, species, and genotype (Collantes et al, 1999;Agerbirk et al, 2003;Hol et al, 2004), age of plant (Hara et al, 2000;Frolich et al, 2006), and ontogenetic stage of the tissues (Ohnmeiss and Baldwin, 2000;Walls et al, 2005). Moreover, variability between root and shoot defensive chemical concentration can be explained by abiotic factors such as atmospheric CO 2 , N 2 , light, and site of origin (Wainhouse et al, 1998;Mattson et al, 2005).…”