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    Author(s): Joy K. Ward; John M. Harris; Thure E. Cerling; Alex Wiedenhoeft; Michael J. Lott; Maria-Denise Dearing; Joan B. Coltrain; James R. Ehleringer
    Date: 2005
    Source: Proceedings of the National Academy of Sciences of the United States of America. Vol. 102, no. 3 (Jan. 18, 2005): p. 690-694.
    Publication Series: Miscellaneous Publication
    PDF: Download Publication  (199 KB)


    The Rancho La Brea tar pit fossil collection includes Juniperus (C3) wood specimens that 14C date between 7.7 and 55 thousand years (kyr) B.P., providing a constrained record of plant response for southern California during the last glacial period. Atmospheric CO2 concentration ([CO2]) ranged between 180 and 220 ppm during glacial periods, rose to 280 ppm before the industrial period, and is currently approaching 380 ppm in the modern atmosphere. Here we report on [delta]13C of Juniperus wood cellulose, and show that glacial and modern trees were operating at similar leaf- intercellular [CO2](ci)/atmospheric [CO2](ca) values. As a result, glacial trees were operating at ci values much closer to the CO2-compensation point for C3 photosynthesis than modern trees, indicating that glacial trees were undergoing carbon starvation. In addition, we modeled relative humidity by using [delta]18O of cellulose from the same Juniperus specimens and found that glacial humidity was 10% higher than that in modern times, indicating that differences in vapor-pressure deficits did not impose additional constrictions on ci/ca in the past. By scaling ancient ci values to plant growth by using modern relationships, we found evidence that C3 primary productivity was greatly diminished in southern California during the last glacial period.

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    Ward, Joy K.; Harris, John M.; Cerling, Thure E.; Wiedenhoeft, Alex; Lott, Michael J.; Dearing, Maria-Denise; Coltrain, Joan B.; Ehleringer, James R. 2005. Carbon starvation in glacial trees recovered from the La Brea tar pits, southern California. Proceedings of the National Academy of Sciences of the United States of America. Vol. 102, no. 3 (Jan. 18, 2005): p. 690-694.


    Low CO2, paleoclimate, Juniperus, ci/ca, ancient wood, ancient NPP, radiocarbon dating, carbon isotopes, humidity, climatic changes, fossil trees, juniper, paleobotany, vapor pressure, carbon dioxide, tar pits, La Brea Pits (Calif.)

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