Carbon isotope discrimination in the C4 desert shrub Atriplex confertifolia has been suggested as an accurate indicator of past atmospheric carbon isotope composition and, therefore, as a potentially useful tool in modeling the global carbon cycle. This use however hinges on the assumption that photosynthetic discrimination (D13C) remains constant under varying environmental conditions. There have been no previous controlled experiments studying the influence of environmental factors on D13C in Atriplex confertifolia. In this study, a nested 2 X 2 factorial growth chamber experiment used 139 Atriplex confertifolia plans to test the effect on carbon isotope discrimination of different levels of light and water within a linked CO2, relative humidity, and temperature regine. Carbon isotope discrimination varied greatly between the two regimes and both regime and light were found to significantly influence discrimination. Water was found to be a non significant factor. No interaction between the factors was found. A consistent pattern of D13C variation was found among the water-by-light treatments. The highest D13C values were found in the High Water-Low Light (HL) and Low Water-Low Light (LL) treatments. Lower values were consistently found in the Low Water-High Light (LH) and High Water-High Light (HH) treatments. These preliminary results do not support the assumption that D13C in Atriplex confertifolia remains constant under varying environmental conditions.
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Last updated: 8 January 2001, KAK.