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Title: RESPONSE OF PLANTS TO ELEVATED ATMOSPHERIC CO2

Author
item Kimball, Bruce

Submitted to: Indian Journal of Plant Physiology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 6/15/2002
Publication Date: 1/15/2003
Citation: Kimball, B.A. 2003. Response of plants to elevated atmospheric co2. Indian Journal of Plant Physiology (Special Issue), pp. 18-24.

Interpretive Summary: In order to determine the likely effects of the increasing atmospheric CO2 concentration on the physiology, growth, yield, water use, and soil carbon sequestration of agricultural crops under open-field conditions, free-air CO2 enrichment (FACE) experiments have been conducted in Arizona, USA; Switzerland; Italy; and Japan. Since the first in 1989, the experiments have been conducted on cotton, wheat, sorghum, ryegrass, white clover, grape, potato, and rice. An exhaustive review was conductive of the results from these experiments, as well as from prior CO2-enrichment experiments conducted in various types of chambers. Generally, the elevated CO2 stimulated growth and yield of all the crops when soil moisture and water were ample, except sorghum. However, sorghum too was stimulated under drought conditions. Generally also, the stimulation due to elevated CO2 was smaller when soil nitrogen was low, except for the white clover, a legume crop which has the ability to obtain nitrogen from symbiotic bacteria. The woody grape and cotton crops were stimulated more than the herbaceous crops. Changes in soil carbon content were difficult to detect in any particular experiment, but averaging overall, there appeared to be an increase in soil carbon storage, which would tend to slow the rate of rise of the atmospheric CO2 concentration. This research should benefit all producers and consumers of food and other agricultural products worldwide.

Technical Abstract: The likely effects of future high levels of atmospheric CO2 on several agricultural crops were summarized using published reports from free-air CO2 enrichment (FACE) experiments. Elevated CO2 increased photosynthesis, biomass production, and yield substantially in C3 species, but little in C4. It decreased stomatal conductance and transpiration in both C3 and C4 species and greatly improved water-use efficiency in all the crops. Growth stimulations were as large or larger under water-stress compared to well-watered conditions. Growth stimulations of non-legumes were reduced at low soil nitrogen, whereas elevated CO2 strongly stimulated the growth of the clover legume both at ample and under low N conditions. Tissue nitrogen concentrations decreased while carbohydrate and some other carbon-based compounds increased due to elevated CO2, with leaves and foliage affected more than other organs. Detection of statistically significant changes in soil organic carbon in any one study was impossible, yet by combining results from several sites and years, it appeared that elevated CO2 did increase sequestration of soil carbon.