Carbon starvation

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 CO2concentration ([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 δ13C of Juniperus wood cellulose, and show that glacial and modern trees were operating at similar leaf-intercellular [CO2](c i)/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 δ18O 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 c i/c a in the past. By scaling ancient c ivalues 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. using modern relationships, we found evidence that C3 primary productivity was greatly diminished in southern California during the last glacial period.

Ward et al., 2005

 

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