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Global Climate Change Digest
A Guide to Information on Greenhouse Gases and Ozone Depletion
Published July 1988 through June 1999

FROM VOLUME 11, NUMBER 10, OCTOBER 1998

PROFESSIONAL PUBLICATIONS...
ELEVATED-CO₂ EFFECTS ON PLANTS

Item #d98oct11

“Interactions of CO₂ Enrichment and Temperature on Cotton Growth and Leaf Characteristics,” K. R. Reddy (Dept. Plant and Soil Sci., Miss. State Univ., Box 9555, Mississippi State, MS, 39762) et al., Env. Exptl. Bot. 39 (27), 117-129 (1998).

The stomatal density and index of upland cotton were not affected by the elevation of atmospheric CO₂ concentration. Leaves were larger in area and had higher biomass under elevated CO₂ at all temperatures. The optimum temperature for vegetative and reproductive growth was not changed by CO₂ concentration. Flower and fruit retentions were severely curtailed by higher temperatures but unaffected by CO₂ concentration, underscoring the need to use species and cultivars that are heat resistant in warmer climates.

Item #d98oct12

“The Effect of Elevated CO₂ Concentration and Nutrient Supply on Carbon-Based Plant Secondary Metabolites in Pinus sylvestris L.,” C. J. Heyworth (MLURI, Craigiebuckler, Aberdeen AB15 6QH, Scotland), et al., Oecologia 115, 344-350 (1998).

Elevated CO₂ increased dry mass per needle, tree height, and monoterpene a-pinene concentration, and the cellulase digestibility of the needles was increased by the high nutrient availability. But, expected increases in atmospheric CO₂ will not be great enough to change the concentrations of tannins and monoterpenes in Scots pine nor influence the secondary processes like decomposition and herbivore food selection.

Item #d98oct13

“Photosynthetic Pathway and Ontogeny Affect Water Relations and the Impact of CO₂ on Bouteloua gracilis (C4) and Pascopyrum smithii (C3),” J. A. Morgan (USDA/ARS, 1701 Centre Ave., Ft. Collins, CO, 80526; morgan@lamar.colostate.edu) et al., Oecologia 114, 483-493 (1998).

In growth-chamber studies, both species exhibited increases in leaf CO₂ assimilation, photosynthesis, transpiration use efficiency, plant growth, and water-use efficiency with elevated CO₂. Effects were more pronounced in the Pascopyrum. Decreased soil-water content was associated with increased sequestering of carbohydrates and the production of more belowground biomass in the Pascopyrum. It also exhibited increased root-to-shoot ratios at elevated CO₂.

Item #d98oct14

“Effects of Climate and Atmospheric CO₂ Partial Pressure on the Global Distribution of C4 Grasses: Present, Past, and Future,” G. J. Collatz (Goddard Space Flight Center, Code 923, Greenbelt, MD, 20771; jcollatz@biome.gsfc.nasa.gov), J. A. Berry, J. S. Clark, Oecologia 114, 441-454 (1998).

Maps were constructed from climatological data sets to classify the globe into areas that favor grasses that use the C4 photosynthetic pathway and thus to model plant-community responses to atmospheric CO₂ concentration. Lowering the CO₂ concentration to preindustrial levels expanded the range of C4 grasses. Conditions during the most recent glacial maximum substantially favored C4 vegetation. Doubling the current CO₂ concentration substantially reduces today’s area of C4 grasses.

Item #d98oct15

“The Effects of Parental CO₂ Environment on Seed Quality and Subsequent Seedling Performance in Bromus rubens,” T. E. Huxman (Dept. Biol. Sci., Univ. Nev. Las Vegas, Las Vegas, NV, 89154; huxman@nye.nscee.edu) et al., Oecologia 114, 202-208 (1998).

Seeds of an exotic annual grass grown under elevated CO₂ had larger pericarp surface areas, higher C:N ratios, and less mass than normal seeds of the species, but their germination ratio and germination time were unchanged. The elevated-CO₂ seeds had smaller seed reserves, exhibited a reduced growth rate, and attained smaller final mass. The higher C:N ratios may severely affect seed quality and seedling performance.

Item #d98oct16

“A Meta-Analysis of Elevated CO₂ Effects on Woody Plant Mass, Form, and Physiology,” P. S. Curtis (Dept. Plant Biol, The Ohio Stat Univ., 1735 Neil Ave., Columbus, OH, 43210; curtis.7@osu.edu), Xianzhong Wang, Oecologia 113, 299-313 (1998).

An integration of the literature on the effects of elevated CO₂ on woody plants indicates that total biomass and net CO₂ assimilation increase significantly at doubled CO₂, regardless of growing conditions. Low soil-nutrient availability reduces the CO₂-fertilization effect, low light increases it, and interacting stress factors do not affect it. No significant shifts are seen in biomass allocation, in stomatal conductance, or in photosynthesis (i.e., no acclimation to the elevated CO₂ occurs). Dark respiration and leaf nitrogen both increase with CO₂ enrichment, and leaf starch content generally decreases.

Item #d98oct17

“Long-Term Responsiveness to Free Air CO₂ Enrich-ment of Functional Types, Species, and Genotypes of Plants from Fertile Permanent Grassland,” A Lüscher (Inst. Plant Sci., Swiss Fed. Inst. technol., CH-8092 Zurich, Switzerland; andreas.luescher@ipw.agrl.ethz.ch), G. R. Hendrey, J. Nösberger, Oecologia 113, 37-45 (1998).

Among grasses, nonleguminous dicots, and legumes, legumes showed the strongest yield increase in response to elevated CO₂ and grasses the weakest. Legume response declined from the first to second year, while nonleguminous- dicot response increased for three years. The grasses and nonleguminous dicots exhibited the strongest response during reproductive growth in the spring. No genotypic differences were observed in response to elevated CO₂. The interspecies differences in temporal distribution of the effects imply that elevated CO₂ would produce complex competitive interactions in mixed communities of these plants.

Item #d98oct18

“Nutrient Relations in Calcareous Grassland Under Elevated CO₂,” P. A. Nicklaus (Inst. Botany, Schönbeinstrasse 6, CH-4056 Basel, Switzerland; niklauspa@unibas.ch) et al., Oecologia 116, 67-75 (1998).

In calcareous grasslands, total biomass nitrogen, total aboveground phosphorus, and tissue N:P ratios were not altered by CO₂ enrichment. In legumes, the C:N ratio was not altered, but the N:P ratio was increased slightly. Although total-plant nitrogen was not affected by elevated CO₂, microbial nitrogen pools increased, and plant-available soil nitrogen decreased. Greenhouse experiments also indicated that plant nitrogen pools were unaffected by elevated CO₂; however, when phosphorus was added along with CO₂ enrichment, total-plant nitrogen pools increased, suggesting a complex interaction among CO₂ concentration, nitrogen availability, and phosphorus supply.

Item #d98oct19

“Effects of Elevated CO₂ and Phosphorus Addition on Productivity and Community Composition of Intact Monoliths from Calcareous Grassland,” Jürg Stöcklin (Inst. Bot., Univ. Basel, Schönbeinstrasse 6, CH-4056 Basel, Switzerland; stoecklin2@unibas.ch), Kathrin Schweizer, Christian Körner, Oecologia 116, 50-56 (1998).

When calcareous grassland was exposed to elevated CO₂ in a greenhouse, aboveground dry mass remained unchanged during the first year but increased significantly in the second year. Belowground biomass was unchanged by the elevated CO₂. The effect on biomass of phosphorus alone was small. Some species (e.g., Bromus erectus) responded negatively to elevated CO₂, and during the second year, the community composition shifted towards species that were more responsive to elevated CO₂. Biomass production at elevated CO₂ was higher when phosphorus was added. These results indicate that interactions among CO₂ concentration, species selection, and nutrient availabilities govern plant-community responses to elevated CO₂.

Item #d98oct20

“Effect of Enhanced Atmospheric CO₂ on Mycorrhizal Colonization by Glomus mosseae in Plantago lanceolata and Trifolium repens,” P. L. Staddon (Dept. Biol., Univ. York, P.O. Box 373, York, YO1 5YW, U.K.; pls101@york.ac.uk), J. D. Graves, A. H. Fitter, New Phytol. 139, 571-580 (1998).

Both species grew faster in elevated CO₂. Elevated CO₂ did not affect the percentage of root length colonized, colonization intensity, or phosphorus inflow, and it did not have any direct permanent effect on mycorrhizal functioning.

Item #d98oct21

“Effects of a Natural Source of Very High CO₂ Concentration on the Leaf Gas Exchange, Xylem Water Potential, and Stomatal Characteristics of Plants of Spatiphylum cannifolium and Bauhinia multinervia,” M. D. Fernández (Cent. Bot. Trop., Inst. Biol. Exptl., Univ. Cent. Venezuela, Apartado 47577, Caracas 1041A, Venezuela; aherra@strix.ciens.ucv.ve) et al., New Phytol. 138, 689-697 (1998).

Xylem water potential was lowered by drought, and elevated CO₂ lowered it further in the Spatiphylum. Plants growing under elevated CO₂ had higher photosynthetic rates, increased water-use efficiency, and depressed stomatal initiation. These factors combined to allow the elevated-CO₂ plants to attain higher carbon balances.

Item #d98oct22

“Elevated CO₂ and Tree Root Growth: Contrasting Responses in Fraxinus excelsior, Quercus petraea, and Pinus sylvestris,” Meg Crookshanks (Sch. Biol. Sci., Univ. Sussex, Falmer, Brighton, Sussex, BN1 9QG, U.K.; g.taylor@sussex.ac.uk), Gail Taylor, Mark Broadmeadow, New Phytol. 138, 241-250 (1998).

Elevated CO₂ significantly increased root growth, with the greatest increase occurring in ash and the smallest in oak. Changes in specific root length suggest that root diameter and/or density were increased. Root dry weight, later root numbers, and mean root diameter were increased in all species. Root respiration rates were significantly reduced in all three. Soluble sugars increased significantly in all species but starch content increased in some and decreased in others.

Item #d98oct23

“Elevated Carbon Dioxide Ameliorates the Effects of Ozone on Photosynthesis and Growth: Species Respond Similarly Regardless of Photosynthetic Pathway or Plant Functional Group,” J. C. Volin (Dept. Forestry, Univ. Wisc., 1630 Linden Dr., Madison, WI, 53706; jvolin@acc.fau.edu), P. B. Reich, T. J. Givnish,New Phytol. 138 (2), 241-250 (1998).

Elevated CO₂ had little effect on the photosynthesis and relative growth rate of two C3 trees, two C3 grasses, and two C4 grasses. High ozone levels depressed photosynthesis, relative growth rate, and root weight ratio in almost all cases, but these effects were not seen when both CO₂ and ozone levels were elevated. High-stomatal-conductance species were the most susceptible to oxidant damage. Elevated CO₂ reduces stomatal conductance and might, therefore, reduce the damage caused by oxidants.

Item #d98oct24

“Effects of Nitrogen and Water Limitation and Elevated Atmospheric CO₂ on Ectomycorrhiza of Longleaf Pine,” G. B. Runion (Sch. Forestry, 108 M. White Smith Hall, Auburn Univ., AL, 36849; runion@forestry.auburn.edu) et al., New Phytol. 137, 681-689 (1998).

Seedlings grown in elevated CO₂, low nitrogen, and adequate water had almost double the normal numbers of ectomycorrhizal short roots and ectomycorrhizas, but these results occurred only when the nitrogen concentration was elevated.

Item #d98oct25

“Nitrogen Balance for Wheat Canopies (Triticum aestivum cv. Veery 10) Grown Under Elevated and Ambient CO₂ Concentrations,” D. R. Smart (Dept. Veg. Crops, Univ. Calif., 1 Shields Ave., Davis, CA, 95616; drsmart@vegmail.ucdavis.edu) et al., Plant Cell Env. 21, 753-763 (1998).

Wheat plants grown under elevated CO₂ increased carbon allocation to root biomass production and root-zone nitrate consumption but not biomass nitrogen content. Instead, nitrogen loss increased. This diminished nitrate assimilation explains why organic nitrogen contents of plants decline in elevated CO₂.

Item #d98oct26

“The Stomatal Response to CO₂ Is Linked to Changes in Guard Cell Zeaxanthin,” J. Zhu (Dept. Biol., Univ. Calif., Los Angeles, CA, 90095; zeiger@biology.ucla.edu) et al., Plant Cell Env. 21, 813-820 (1998).

Elevated CO₂ decreased zeaxanthin content in leaves and decreased stomatal apertures under lighted conditions. In the dark, however, the changes in stomatal aperture caused by elevated CO₂ were much smaller, and the concentration of guard-cell zeaxanthin did not change. These results indicate that CO₂-produced changes in zeaxanthin content modulate stomatal responses to CO₂ in the light while another mechanism modulates CO₂ response in the dark.

Item #d98oct27

“Response of Sugar Beet (Beta vulgaris L.) Yield and Biochemical Composition to Elevated CO₂ and Temperature at Two Nitrogen Applications,” H. Demmers-Derks (Biochem. Physiol. Dept., IACR-Rothamsted, Harpenden, Hertfordshire, AL5 2JQ, U.K.) et al., Plant Cell Env. 21, 829-836 (1998).

Elevated CO₂ increased total dry mass at harvest by 21% under high-nitrogen and 11% under low-nitrogen conditions. The respective increases in root dry mass were 26% and 12%. Warmer temperatures, however, decreased both total and root dry masses. Neither elevated CO₂ or temperature influenced root sucrose concentration. Amino acids decreased in elevated CO₂ and increased in warmer temperatures.

Item #d98oct28

“Tansley Review No. 98: Tree and Forest Functioning in an Enriched CO₂ Atmosphere,” Henrik Saxe (Inst. Bot., Dendrol., Forest Gen., The Arboretum The Royal Vet. and Ag. Univ., Kirkegaardsvej 3A, DK-2970, Hoersholm, Denmark; hsa@kvl.dk), D. S. Ellsworth, James Heath, New Phytol. 139 (3), 395-436 (1998).

A review of the literature reveals a significantly larger long-term increase in biomass for conifers than for deciduous trees under elevated CO₂, although stimulation of photosynthesis was similar and larger than previously believed. The many down-regulation pathways make predicting growth and canopy CO₂ exchange uncertain, and the down-regulation of photosynthesis is rarely large enough to offset the photosynthetic gains. The response of stomatal conductance to elevated CO₂ in trees is very different from that in herbaceous species. Canopy transpiration is affected positively by changes in leaf area and negatively by changes in stomatal aperture. Elevated CO₂ can alter tree-soil interactions and, thus, ecosystem productivity. Moreover, changes in foliage carbon, mineral nutrients, and secondary metabolites brought about by elevated CO₂ can influence tree-insect interactions. In most trees, mycorrhizal interactions are affected more by nutrient deficiencies than they are by CO₂ concentration.