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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 9, NUMBER 3, MARCH 1996

PROFESSIONAL PUBLICATIONS...
IMPACTS OF CO₂

Item #d96mar19

"A Meta Analysis of Leaf Gas Exchange and Nitrogen in Trees Grown Under Elevated Carbon Dioxide," P.S. Curtis (Dept. Plant Biol., Ohio State Univ., 1735 Neil Ave., Columbus OH 43210), Plant, Cell & Environ., 19(2), 127-137, Feb. 1996.

This review of studies published through May 1994 and of several unpublished works, commissioned by the journal, is the first meta analysis of its type and provides statistical confirmation of several responses of trees to elevated CO₂. It also highlights important areas of continued uncertainty. Overall, net CO₂ assimilation showed a large and significant increase at elevated CO₂, but length of CO₂ exposure and the exposure facility were important modifiers of this response. Other responses studied are stomatal conductance, leaf dark respiration, and leaf nitrogen or specific leaf area in woody plants.

Item #d96mar20

"The Effects of Long-Term Elevation of Air Temperature and CO₂ on Frost Hardiness of Scots Pine," T. Repo (Faculty of Forestry, Univ. Joensuu, POB 111, FIN-80101 Joensuu, Finland), ibid., 209-216.

Studied 20- to 25-year-old saplings for two years. The risks of frost damage are marked in the predicted climatic conditions in Finland, and depend on how the occurrence of the frost episodes changes with respect to climatic warming during the annual cycle, especially in autumn and spring. Conditions in mid-winter are not thought to be critical for frost injury to trees in the future.

Item #d96mar21

"Effects of Elevated CO₂, Elevated O3 and Potassium Deficiency on Norway Spruce [Picea abies (L.) Karst.]: Seasonal Changes in Photosynthesis and Non-Structural Carbohydrate Content," J.D. Barnes (Dept. Agric. & Environ. Sci., Ridley Bldg,. Univ. Newcastle upon Tyne NE1 7RU, UK), T. Pfirrmann et al., ibid., 18(12), 1345-1357, Dec. 1995.

Studied two clones of 5-year-old trees exposed for one season (Apr. to Oct.) in a phytotron that recreated an artificial climate similar to that at a high elevation site in the Inner Bavarian Forest. Parameters measured included rate of net CO₂ assimilation by needles of various ages, chlorophyll fluorescence kinetics, and seasonal changes in non-structural carbohydrates. The measured effects emphasize the need to take into account not only soil nutrient status, but also the impact of concurrent increases in photochemical oxidant pollution in any serious consideration of the effects of climate change on plant production.

Item #d96mar22

"Inter- and Intra-Generic Difference in Growth, Reproduction and Fitness of Nine Herbaceous Annual Species Grown in Elevated CO₂ Environments," E.J. Farnsworth (Dept. Organismic & Evolutionary Biol., Harvard Univ. Herbaria, 22 Divinity Ave., Cambridge MA 02138), F.A. Bazzaz, Oecologia, 104(4), 454-466, 1995.

Studied how CO₂ (350 or 700 ppm) affected reproduction and growth of herbaceous annual plants with various floral morphologies from the genera Polygonum, Ipomoea, and Cassia. Measured vegetation growth, vegetation biomass at first flowering, and viability and germination of seeds. These varied among the genera, but species within genera typically responded more consistently to CO₂ than did unrelated species. Cogeners may respond similarly in terms of reproductive output under global change, but fitness and prognoses of population persistence and evolutionary performance can be inferred only rarely from examining only vegetative characters.

Item #d96mar23

"Seedling Density Modifies the Growth Responses of Yellow Birch Maternal Families to Elevated Carbon Dioxide," P.M. Wayne (address, previous entry), F.A. Bazzaz, Global Change Biol., 1(5), 315-324, Oct. 1995.

Studied seedling growth responses to CO₂ at 350 and 750 ppm of three maternal families of Betula alleghaniensis, raised individually and in high-density stands. Seedlings in competitive, dense stands showed markedly lower average CO₂-induced growth enhancements than individually grown plants. Maternal families differed in their responses; families showing the greatest response at low density exhibited the least CO₂ responsiveness at high density. The data are examined in terms of the reliability of estimates of CO₂ fertilization potential based solely on individually grown plants, and the potential evolutionary consequences of rising CO₂ on regenerating forest tree populations.

Item #d96mar24

"Simple Carbon Assimilation Response Functions from Atmospheric CO₂, and Daily Temperature and Shortwave Radiation," D.S. Wilks (Dept. Soil, Crop & Atmos. Sci., Cornell Univ., Ithaca NY 14853), D.W. Wolfe, S.J. Riha, ibid., 337-346.

The approach of using a global CO₂ fertilizer effect multiplier in crop or ecosystem models does not take into account the interactions among CO₂, temperature and light on assimilation. This study used a mechanistic model of the biochemistry of photosynthesis to represent the responses of net assimilation to varying parameters. The calculated CO₂ fertilizer effect is greatest at high light levels and warm temperatures. The summary functions determined are suitable for incorporating into crop or ecosystem models for predicting carbon assimilation or biomass production on a daily time step.

Item #d96mar25

"Species Diversity and Ecosystem Response to Carbon Dioxide Fertilization: Conclusions from a Temperate Forest Model," B.M. Bolker (Dept. Ecol. & Evolutionary Biol., Guyot Hall, Princeton Univ., Princeton NJ 08544), S.W. Pacala et al., ibid., 373-381.

Looked at the dynamics of a model of temperate forest growth under doubled CO₂ by combining a detailed, field-calibrated model of forest dynamics with greenhouse data on the range of seedling biomass growth response. Although the model omits many feedbacks and mechanisms associated with climate change, it suggests the large potential effects that species differences and feedbacks can have in ecosystem models, and reinforces the possible importance of diversity to ecosystem function over time scales within the planning horizon for global change policy.

Item #d96mar26

"Towards a Better Experimental Basis for Upscaling Plant Responses to Elevated CO₂ and Climate Warming," Ch. Körner (Inst. Botany, Univ. Basel, CH-4056 Basel, Switz.), Plant, Cell & Environ., 18(10), 1101-1110, Oct. 1995.

Few of the most common assumptions used in modeling plant and ecosystem responses to elevated CO₂ and temperatures have been tested under realistic life conditions. Identifies unexpected discrepancies between predictions and experimental findings, which indicate that a better empirical basis is required for predictions. Offers ten suggestions for improving our ability to scale up from experimental conditions to the real world.

Item #d96mar27

"Leaf and Canopy Responses to Elevated CO₂ in a Pine Forest Under Free-Air CO₂ Enrichment," D.S. Ellsworth (Dept. Applied Sci., Brookhaven Natl. Lab., Upton NY 11973), R. Oren et al., Oecologia, 104(2), 139-146, 1995.

Studied an intact Pinus taeda forest ecosystem. Leaf net photosynthetic rate at 550 ppm CO₂ was enhanced by about 65% compared to the rate at ambient CO₂ (350 ppm). However, longer-term CO₂ responses and feedbacks remain to be evaluated.

Item #d96mar28

"Increased Growth Efficiency of Quercus alba Trees in a CO₂-Enriched Atmosphere," R.J. Norby (Environ. Sci. Div., Oak Ridge Natl. Lab., POB 2008, Oak Ridge TN 37831), S.D. Wullschleger et al., New Phytol., 131(1), 91-97, Sep. 1995.

Experimental observations of small trees in CO₂-enriched atmospheres must be interpreted carefully if they are to be relevant to the potential responses of forest trees. White oak saplings were grown for four seasons in open top chambers with different CO₂ partial pressures. The saplings produced 58% more dry mass in 50 Pa CO₂ and 135% more in 65 Pa compared with those at ambient (35 pa) CO₂. There was not a sustained effect of CO₂ on relative growth rate after the first year, and the increased absolute growth rate could persist only as long as leaf area could increase. Nevertheless, annual stem wood production per unit area (growth efficiency) was 37% greater in elevated CO₂, a response consistent across diverse studies, implying a potential increase in carbon sequestration by forests.

Item #d96mar29

"Terrestrial Higher-Plant Response to Increasing Atmospheric [CO₂] in Relation to the Global Carbon Cycle," J.S. Amthor (Lawrence-Livermore Natl. Lab., L-256, POB 808, Livermore CA 94550), Global Change Biol., 1(4), 243-274, Aug. 1995.

This paper, commissioned by the journal, reviews terrestrial plant responses to CO₂ as they relate to fluxes and pools of carbon in terrestrial plants, soils and the atmosphere. Emphasizes feedbacks on the increase in global CO₂ and their role in the global carbon cycle. Most plant responses to elevated CO₂ act as negative feedbacks.

Item #d96mar30

"The Effects on Arbutus unedo L. of Long-Term Exposure to Elevated CO₂," M.B. Jones (Dept. Botany, Trinity College, Univ. Dublin, Dublin 2, Ireland), J.C. Brown et al., ibid., 295-302.

This sclerophyllous evergreen has been found close to natural CO₂ vents in Italy where the mean CO₂ concentration is 2200 ppm. Compared trees growing in elevated and ambient CO₂ concentrations to test for evidence of adaptation. Looked at stomatal density, stomatal conductance in different seasons, and chlorophyll fluorescence. Since analysis of A/Ci curves showed no evidence of upward or downward regulation of photosynthesis at elevated CO₂, A. unedo is expected to have higher growth rates as ambient CO₂ increases.

Item #d96mar31

"Soil and Biomass Carbon Pools in Model Communities of Tropical Plants Under Elevated CO₂," J.A. Arnone III (Dept. Botany, Univ. Basel, Schönbeinstr. 6, CH-4056 Basel, Switz), Ch. Körner, Oecologia, 104(1), 61-71, 1995.

Reports experiments conducted in greenhouses with somewhat nutrient-limited model communities of moist tropical plant species. Finds that: enormous amounts of carbon can be deposited in the ground that are not normally accounted for in estimates of net primary productivity and net ecosystem productivity; any enhancement of carbon sequestration under elevated CO₂ may be substantially smaller than is currently believed; species dominance in plant communities is likely to change under elevated CO₂, but changes may be slow.