Carbon Dioxide, Populations, and Communities (Physiological Ecology)
Protein concentrations in plant tissues are closely tied to plant nitrogen status. Changes in plant tissue nitrogen are therefore likely to have important effects on species at higher trophic levels. This can lead to increased consumption of plant tissues as herbivores compensate for decreased food quality Stiling and Cornelissen Effects on human nutrition are likely as well.
The preceding discussion has presented the average effects of elevated CO 2 , but obscures important patterns of difference in response among plant species. One of the most important determinants of species differences in response to elevated CO 2 is photosynthetic type. Other species use either of two physiologically distinct processes known as C 4 and CAM photosynthesis Figure 2. C 4 plants include most tropical and sub-tropical grasses and several important crops, including maize corn , sugar cane, sorghum, and the millets. Since CO 2 concentrations are already high within the bundle sheath cells, increasing atmospheric CO 2 concentrations above current levels has little direct effect on photosynthetic rates for C 4 species.
C 4 species do respond to elevated CO 2 by decreasing stomatal conductance; this may lead to some indirect enhancement of photosynthesis by helping avoid water stress under drought conditions Leakey While there is little FACE data available on effects of elevated CO 2 on plant nitrogen and protein concentrations, data from chamber experiments shows C 4 plants to be much less responsive than C 3 plants in this regard Cotrufo et al.
The picture that emerges is that C 4 plants are in general relatively unresponsive to elevation of atmospheric CO 2 above current ambient levels. In contrast to C 4 species, another group of plants, legumes members of the botanical family Fabaceae may be especially capable of responding to elevated CO 2 with increased photosynthesis and growth Rogers et al. For most plants, growth under elevated CO 2 can alter the internal balance between carbon obtained in extra quantities through enhanced photosynthesis and nitrogen either unaffected or taken up in decreased amounts due to decreased uptake of water.
Effects of Rising Atmospheric Concentrations of Carbon Dioxide on Plants
These bacteria are able to "fix" atmospheric nitrogen, chemically reducing it to a form that can be taken up and used by plants. Under elevated CO 2 conditions, legumes may be able to shunt excess carbon to root nodules where it can serve as a carbon and energy source for the bacterial symbionts.
In effect, legumes may be able to exchange the excess carbon for nitrogen and thereby maximize the benefits of elevated atmospheric CO 2. Many studies in controlled environments have shown that, compared to other plant species, legumes show greater enhancement of photosynthesis and growth by elevated CO 2 Rogers et al.
Decreases in tissue nitrogen concentrations under elevated CO 2 are also smaller for legumes than for other C 3 species Cotrufo et al. In FACE experiments, soybeans a legume show a greater response to elevated CO 2 than wheat and rice in photosynthesis and overall growth, although not in harvestable yield Long et al.
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Current evidence suggests that that the concentrations of atmospheric CO 2 predicted for the year will have major implications for plant physiology and growth. Under elevated CO 2 most plant species show higher rates of photosynthesis, increased growth, decreased water use and lowered tissue concentrations of nitrogen and protein. Rising CO 2 over the next century is likely to affect both agricultural production and food quality.
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The effects of elevated CO 2 are not uniform; some species, particularly those that utilize the C 4 variant of photosynthesis, show less of a response to elevated CO 2 than do other types of plants. Rising CO 2 is therefore likely to have complex effects on the growth and composition of natural plant communities. Ainsworth, E. Rice production in a changing climate: a meta-analysis of responses to elevated carbon dioxide and elevated ozone concentration. Global Change Biology 14 , A meta-analytic review of the responses of photosynthesis, canopy properties and plant production to rising CO 2.
New Phytologist , The response of photosynthesis and stomatal conductance to rising CO 2 : mechanisms and environmental interactions. Plant, Cell and Environment 30 , Bloom, A. Carbon dioxide inhibits nitrate assimilation in wheat and Arabidopsis. Science , Cotrufo, M. Elevated CO 2 reduces the nitrogen concentration of plant tissues.
Global Change Biology 4 , Feng, Z. Impact of elevated ozone concentration on growth, physiology and yield of wheat Triticum aestivum L. Interactions between plant growth and soil nutrient cycling under elevated CO 2 : a meta-analysis. Global Change Biology 12 , Jablonski, L. Plant reproduction under elevated CO 2 conditions: a meta-analysis of reports on 79 crop and wild species.
Keeling, R. Department of Energy, Leakey, A.
Journal of Experimental Botany 60 , Loladze, I. Rising atmospheric CO 2 and human nutrition: toward globally imbalanced plant stoichiometry? Long, S. Food for thought: Lower-than-expected crop yield stimulation with rising CO 2 concentrations. Marschner, H. Mineral Nutrition of Higher Plants , 2nd ed. London, UK: Academic Press, Morgan, P. How does elevated ozone impact soybean? A meta-analysis of photosynthesis, growth and yield. Plant, Cell and Environment 26 , Poorter, H.
Plant growth and competition at elevated CO 2 : on winners, losers and functional groups.
Rogers, A. Will elevated carbon dioxide concentration amplify the benefits of nitrogen fixation in legumes? Plant Physiology , Stiling, P. How does elevated carbon dioxide CO 2 affect plant-herbivore interactions? A field experiment and meta-analysis of CO 2 -mediated changes on plant chemistry and herbivore performance.
Examining Plant Physiological Responses to Climate Change through an Evolutionary Lens
Global Change Biology 13 , Taub, D. Effects of elevated CO 2 on the protein concentration of food crops: a meta-analysis. Why are nitrogen concentrations in plant tissues lower under elevated CO 2? A critical examination of the hypotheses.
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