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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 12, NUMBER 5, MAY 1999

CO2 FERTILIZATION

Item #d99may4

“Gas Exchange and Chlorophyll Fluorescence Responses of Three Southwestern Yucca Species to Elevated CO₂ and High Temperature,” T. E. Huxman et al., Plant, Cell and Environment, 21 (12), 1275-1283 (1998).

Coastal C3, desert C3, and desert CAM yucca plants were exposed to elevated CO₂ and high temperatures. The coastal species experienced decreased carboxylation efficiency and a 33% decrease in CO₂ saturated maximum assimilation rate. Its elevated-CO₂-induced enhanced photosynthesis lasted four days before reverting. The desert species showed no such changes.

Item #d99may5

“Sap Flow in Scots Pines Growing Under Conditions of Year-Round Carbon Dioxide Enrichment and Temperature Elevation,” S. Kellomäki and K.-Y. Wang, Plant, Cell and Environment, 21 (10), 969-981 (1998).

Thirty-year-old Scots pines were subjected to increased CO₂ and temperature in closed-top chambers. Enhanced CO₂ caused an overall 14.4% decrease in diurnal sap flow, indicating an influence on seasonal water use. Elevated temperature increased overall sap flow by 32.5%, which was attributed to temperature-induced increases in needle area and decreased stomatal sensitivity to high vapor-pressure deficit.

Item #d99may6

“Stomata of Trees Growing in CO₂-Enriched Air Show Reduced Sensitivity to Vapour Pressure Deficit and Drought,” J. Heath, Plant, Cell and Environment, 21 (11), 1077-1088 (1998).

Stomatal conductance in oak was decreased by elevated CO₂; but under elevated CO₂, the stomata of beech and chestnut did not close normally with vapor pressure deficit and during drought. Under enhanced CO₂, the photosynthesis rate of beech and chestnut increased only under high irradiance and with beech was greatest under drought conditions. Thus, carbon gain was made at the expense of water-use efficiency specifically when water conservation was important, indicating serious consequences in terms of drought tolerance under enhanced-CO₂ conditions.

Item #d99may7

“Photosynthetic Down-Regulation in Larrea tridentata Exposed to Elevated Atmospheric CO₂: Interaction with Drought Under Glasshouse and Field (FACE) Exposure,” T. E. Huxman et al., Plant, Cell and Environment, 21 (11), 1153-1161 (1998).

A Mojave Desert shrub was subjected to enhanced CO₂ and varying water conditions. When well watered, it down- regulated its photosynthesis under enhanced CO₂. Under drought conditions, CO₂ concentration did not affect the maximum photosynthesis rate or the carboxylation efficiency, both of which decreased in response to the drought. But, Rubisco catalytic sites decreased under drought, resulting in greater photosynthesis rates under enhanced CO₂. These results indicate that drought can reduce down-regulation and produce seasonal carbon gains in response to enhancement of CO₂ concentrations and that water availability may determine the photosynthesis response of desert ecosystems to increased CO₂.

Item #d99may8

“Elevated CO₂ Enhances Stomatal Responses to Osmotic Stress and Abscisic Acid in Arabidopsis thaliana,” J. Leymarie, G. Lascève, and A. Vavsseur, Plant, Cell and Environment, 22(3), 301-308 (1998).

In Arabidopsis thaliana, a doubling of CO₂ concentration produces a rapid drop in leaf conductance that is almost completely reversed in two photoperiods. But the decrease in leaf conductance caused by osmotic stress is strongly enhanced by enhanced CO₂, and that caused by the application of abscisic acid to the roots is also stronger.