WELLINGTON, Nov. 28 (Xinhua) -- Scientists at Auckland-based Unitec Institute of Technology have compared historic native leaf samples taken during Captain Cook's first visit to New Zealand nearly 250 years ago with modern day samples to see if they have changed with atmospheric CO2.
Unitec Associate Professor Mark Lange said on Tuesday that the tests showed a critical change in atmospheric carbon dioxide (CO2) after the 19th Century, a result reflected in studies of northern hemisphere plants.
"However, this has been a unique opportunity to look at some of the oldest herbarium specimens collected in the southern hemisphere," Lange said in a statement.
These precious plants which survived the long voyage aboard HMS Endeavour in returning to Britain, provide researchers with a unique record of the New Zealand environment before the rise in atmospheric CO2 levels, he said.
Unitec researchers were looking for changes in the density of microscopic pores called stomata, which regulate the intake or release of CO2, oxygen, and water vapor. The higher the CO2 concentration, the lower the number of pores.
Links have been shown between the levels of CO2 in the surrounding atmosphere and the density of stomata on certain plants, Lange said.
When Captain Cook made his first voyage to the South Pacific during 1769-1770, he was accompanied by two botanists, Joseph Banks and Daniel Solander who gathered samples as they travelled, which were sent to the British Museum in 1828. Sets of these samples numbering 313 species are now held at Auckland War Memorial Museum and the Museum of New Zealand.
Of the hundreds of samples collected by Banks and Solander, Unitec researchers found leaves from the Karaka tree were the most suitable, having remained intact and with good sized leaves which clearly showed the stomata.
The study showed little variation of stomatal density between the 18th to 19th century leaf samples, but when the modern samples were analyzed, they showed a decrease in stomatal density of up to 53 percent, which corresponds to an increase in atmospheric CO2 over that time, according to Lange. Enditem
