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Politics : Formerly About Advanced Micro Devices -- Ignore unavailable to you. Want to Upgrade?

To: J_F_Shepard who wrote (826578)	12/29/2014 8:01:44 PM
From: Brumar89	1 Recommendation Recommended By FJB Read Replies (1) \| Respond to of 1578548

Wrong: *Atmospheric CO2 concentration ([CO2]) ranged between 180 and 220 ppm during glacial periods* The study below cited the low CO2 level during the last ice age. Carbon starvation in glacial trees recovered from the La Brea tar pits, southern California Pertenece a: PubMed Central (PMC) PubMed Central (PMC3 - NLM DTD) Descripción: 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 ppmin the modern atmosphere. Here we report on ?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 ?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. http://biblioteca.universia.net/html_bura/ficha/params/title/carbon-starvation-in-glacial-trees-recovered-from-the-brea-tar/id/912067.html