The high carbon-to-nitrogen ratio in these plants means that they are nitrogen-deficient, because a greater amount of nitrogen is needed to sustain the larger plant.

Bazzaz has also found that some types of plants, including corn and sugar cane, stop growing faster earlier than weeds and crops such as wheat and soybeans.

Consequently, higher levels of carbon dioxide in the atmosphere mean that corn, which is surrounded by a denser growth of weeds, requires more herbicides. Wheat, however, which is more nitrogen-deficient and slightly less healthy, requires higher doses of fertilizer.

Ecosystem Affected

The nitrogen deficiency will not only affect the plants, but the ecosystem as well, Bazzaz says.

First, with the amount of nitrogen in plant tissues decreasing, the circulation of nutrients in nature will slow down.

Trees normally get their nitrogen from the ground and convert it to protein. When tree leaves fall onto the ground, they are decomposed by microorganisms into nutrients and nitrogen, which are then reused by the trees the following season.

Experiments in the Harvard Forest Ecosystem near Petersham, Mass. have shown that if there is too much carbon in the leaves, decomposition slows down, and nutrients are returned to the ground more slowly. Once there are less nutrients in the ground, plant growth will be stunted.

Secondly, Bazzaz has shown in experiments that butterfly larvae that eat leaves with a higher carbon-to-nitrogen ratio than normal are more prone to death. They have a higher mortality rate and grow less than larvae that eat leaves grown from a nitrogen-rich environment. Consequently, insect populations will go down, which in turn may upset the food chain.

It may very well turn out that some species of plants and insects may become extinct as carbon dioxide levels in the atmosphere continue to increase, says Bazzaz.

"If you increase carbon dioxide, plants have different responses: some become more dominant and other less dominant," says Bazzaz. "This could reduce plant diversity and filter down to animals."

Bazzaz proposes that cutting down on fuel consumption could be a significant factor in reducing carbon dioxide in the atmosphere. "We need to be more efficient," he says. "We need to move towards alternative energy sources such as solar energy."