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Title: RESPONSES OF AGRICULTURAL CROPS TO FREE-AIR CO2 ENRICHMENT

Author
item Kimball, Bruce
item KOBAYASHI, K - NIAS, TSUKUBA JAPAN
item BINDI, M - UNIV FLORENCE, ITALY

Submitted to: Advances in Agronomy
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 7/20/2001
Publication Date: 3/1/2002
Citation: N/A

Interpretive Summary: To determine the likely effects of the increasing atmospheric carbon dioxide (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 conducted 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. Also, the stimulation due to elevated CO2 was smaller generally when soil nitrogen was low, except for white clover, a legume crop that can obtain nitrogen from 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 on averagr, there appeared to be an increase in soil carbon storage, which would tend to slow the rate of rise of atmospheric CO2. 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 investigated. Using literature reports from free-air CO2 enrichment (FACE) experiments, the relative responses of the crops were extracted, tabulated, and analyzed with regard to many plant and soil processes. Elevated CO2 increased photosynthesis and biomass production and yield substantially in C3 species, but little in C4; and 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. Root growth was generally stimulated more than that of shoots. Woody perennials had the largest growth responses to elevated CO2. 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 appears that elevated CO2 did increase sequestration of soil carbon. With only two exceptions, comparisons between the FACE-based data and those from reviews of prior chamber-based data were consistent, which gives confidence that conclusions drawn from both types of data are accurate. However, the more realistic FACE environment and the larger plot size enabled more extensive robust multidisciplinary data sets to be obtained under conditions representative of open fields in the future high-CO2 world.