Skip to main content
ARS Home » Research » Publications at this Location » Publication #128736
Title: THE EFFECT OF LONG-TERM ATMOSPHERIC CO2 ENRICHMENT ON THE INTRINSIC WATER-USE EFFICIENCY OF SOUR ORANGE TREES

Author
item LEAVITT, S - UNIV OF ARIZONA
item IDSO, S - USDA-ARS-USWCL PHOENIX AZ
item Kimball, Bruce
item BURNS, J - UNIV OF ARIZONA
item SINHA, A - UNIV OF S CALIFORNIA
item STOTT, L - UNIV OF S CALIFORNIA

Submitted to: Chemosphere
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 1/3/2001
Publication Date: 6/15/2003
Citation: Leavitt, S.W., Idso, S.B., Kimball, B.A., Burns, J.M., Sinha, A., Stott, L. 2003. The effect of long-term atmospheric co2 enrichment on the intrinsic water-use efficiency of sour orange trees. Chemosphere. 50:217-222.

Interpretive Summary: As the air's CO2 content continues to rise, there is concern that consequent changes in climate could lead to localized decreases in moisture needed to sustain the growth of trees and their ability to sequester carbon. We studied this subject as part of what has become the longest atmospheric CO2 enrichment experiment ever conducted. After 13 years of growth in clear-plastic-wall open-top chambers continuously supplied with air of either 400 or 700 ppm CO2, we extracted four radial wood cores from the trunk of each of the four trees that grew in each of the two CO2 treatments and measured their stable carbon isotope concentrations. We found that the trees of the CO2-enriched chambers had water use efficiencies that were 80% greater than those of the trees growing in the ambient CO2 chambers. This result is identical to the mean CO2-induced water use efficiency increase reported for 23 groups of naturally-occurring trees scattered throughout western North America and suggests that Earth's trees should be well protected against any reduction in moisture availability that might result from potential global climate change. This finding should be of great significance to policymakers who are attempting to develop effective national and international programs to slow the rate of rise of the air's CO2 content and forestall global warming.

Technical Abstract: Every two months in 1992, as well as on three occasions in 1994-5, we obtained leaf samples together with samples of surrounding air from eight well-watered and fertilized sour orange (Citrus aurantium L.) Trees that were growing out-of-doors in Phoenix, Arizona, USA. These trees had been planted in the ground as small seedlings in July 1987 and enclosed in pairs by four clear-plastic-wall open-top chambers of which two have been continuously maintained since November of that year at a CO2 concentration of 400 umol mol-1, and two have been maintained at 700 umol mol-1. In September 2000, we also extracted north-south and east-west oriented wood cores that passed through the center of each tree's trunk at a height of 45 cm above the ground. Stable-carbon isotope ratios (13C/12C) derived from these leaf, wood and air samples were used to evaluate each tree's intrinsic water-use efficiency (iWUE). The grand-average result was an 80% increase in this important plant parameter in response to the 300 umol mol-1 increase in atmospheric CO2 concentration employed in the study. This increase in sour orange tree iWUE is identical to the long-term CO2-induced increase in the trees' production of wood and fruit biomass, which suggests there could be little to no change in total water use per unit land area for this species as the air's CO2 content continues to rise. It is also identical to the increase in the mean iWUE reported for 23 groups of naturally-occurring trees scattered across western North American that was caused by the historical rise in the air's CO2 content that occurred between 1800 and 1985.