Field techniques for exposure of plants and ecosystems to elevated CO2 and other trace gases

Carbon dioxide (CO{sub 2}) concentration of the atmosphere has varied considerably over geological time. Ice core data from the USSR Vostok Station showed that the Earth`s atmospheric CO{sub 2} ranged from as low as 180 to 200 {mu}mol mol{sup {minus}1} during the last two glacial maxima (13,000 to 40,000 and 130,000 to 160,000 years before present). However, following the rapid glacial melting, the concentration rose quickly to about 260 to 270 {mu}mol mol{sup {minus}1}. Since around 1700 AD, the CO{sub 2} concentration has increased from about 270 {mu}mol mol{sup {minus}1} to 315 {mu}mol mol{sup {minus}1} in 1958 and 355 {mu}mol mol{sup {minus}1} in 1991. 209 refs., 4 figs., 2 tabs.