Biologist Studies Effects of Carbon Dioxide on Plants

The heavy industrial pollution and the burning down of large areas of forest land have been increasing the levels of carbon dioxide in the atmosphere for over a century, many scientific studies have shown.

And while these studies have sparked much talk about the Greenhouse Effect, the work of one Harvard biologist points to other adverse environmental effects--that the high carbon dioxide content is making plants less healthy and ultimately throwing the ecosystem off balance.

Timken Professor of Science Fakhri A. Bazzaz has studied the effects of carbon dioxide on plants and plant growth, and has found that more carbon causes plants to grow faster, but deprives them of adequate nutrients.

Increased Pollution, Deforestation

Until the 1800s, carbon dioxide levels in the atmosphere had remained relatively constant for the last 100,000 years, Bazzaz says.

But ever since the industrial revolution in the mid-1800s, carbon dioxide levels have been steadily rising. As industry expands, consumption of fossil fuels rises to meet the demands of that growth, he says.

Scientists have already found a direct correlation between the increase in fossil fuel use and the elevated carbon dioxide levels in the atmosphere. It is estimated that 80 percent of the carbon dioxide emitted into the atmosphere is due to industrial consumption of fossil fuels, while 20 percent is due to deforestation.

Forests are crucial for reducing the amount of carbon dioxide in the atmosphere because they convert carbon dioxide into oxygen through photosynthesis.

But deforestation occurs in many countries where trees are cut and burned to clear land for agriculture. The large-scale burning of the forests gives off high levels of carbon dioxide.

Bazzaz theorizes that carbon dioxide levels will rise exponentially in the near future as underdeveloped countries become industrialized and consume more fossil fuel.

Third-world countries currently consume approximately 2 percent of the fossil fuels that industrialized countries use. As these countries develop in the future, fossil fuel use will skyrocket dramatically.

How Carbon Dioxide Affects Plants

Bazzaz is studying the direct effects of carbon dioxide on different plants and ecosystems.

He has found that increased amounts of carbon dioxide will cause photosynthesis to occur more quickly, which will lead to faster rates of plant growth.

But even though the plants are growing more quickly, they are not as healthy, because they lack sufficient nitrogen, which is converted to plant protein.

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."