Carbon dioxide (CO2) is a natural occurring gas found in trace amounts in the atmosphere. As part of the carbon cycle, many plants, algae and cyanobacteria use CO2 in photosynthesis to produce chemical energy and oxygen as a waste product. Carbon dioxide accumulates in the atmosphere mainly due to the burning of fossil fuels, among other factors. Experts estimate that the global concentration of CO2 will double by the end of the 21st century. Scientists are uncertain about the ultimate impact of CO2 on global climate; however, a worldwide increase of vegetation stimulated by increased CO2 levels has been identified.
In a controlled experiment conducted at a Federal laboratory in Phoenix, Arizona, orange trees were exposed to twice as much concentrations of carbon dioxide for a time period of three years, after which the results showed that the combined volume of their branches and trunks had almost tripled than that of orange trees grown in normal conditions. For some scientists, this is an important improvement in agricultural productivity. This also suggests that an increase in trees and vegetation could help remove excess carbon dioxide, stabilizing its concentrations in the atmosphere.
A new study found that rising levels of CO2 in the atmosphere helps crop plants grow and reproduce; however, the same study states that increased growth and reproduction may affect the nutritional value of crops. Crops have been found to have higher yields whenever sufficient levels of CO2 are present even if the growing conditions are not optimum. The implication is that this result is not balanced between quantity and quality. While production quantities may be higher, the resulting product may be of a lower nutritional quality.
Rising levels of CO2 decrease the nitrogen content of plants, consequently plant eaters, including humans, and animals must consume more vegetables to obtain sufficient amounts of nitrogen-based protein. Nitrogen is an important component for protein building in animals and humans. If the nutritional quality of a plant decreases, people would have to increase their intake of plant food in order to obtain the same health benefits. Under a rising scenario of CO2 levels, both animals and humans would have to increase their intake of plants to compensate for the nutritional loss.
To gain a better understanding at how CO2 may affect plant growth, scientists conducted a meta-analysis technique experiment consisting in gathering together data from various similar studies, summarizing the results. Researchers studied different ways in which plants respond to increased levels of CO2. They found that plants grown at higher concentrations of CO2 had more flowers, more seeds, greater seed weight and lower concentration of nitrogen in the seeds than those grown at normal CO2 levels. The experiments were conducted in greenhouses and chambers; however, plants grown in chambers may not experience the same effects as those grown in a natural setting.
Scientists expect the rising levels of CO2 in the atmosphere to stimulate the growth of a variety of plants. Some scientists suggest that this will trigger abundant vegetation in a global scale; however, others are of the opinion that an explosion in plant growth could be limited by a lack of nutrients and environmental stress. The overall effect could be negative, some researchers say, especially on natural ecosystems. Leaves may not decompose as fast, slowing the release of nutrients and affecting some types of seeds. Other scientists affirm that this could be compensated by an increase of soil microbes and earthworms.
Despite studies carried out to show how CO2 could help agriculture, there is a significant degree of uncertainty as to how plants will respond to increasing levels of atmospheric carbon dioxide. According to the University of California, San Diego, biologists have made significant advances toward understanding the mechanisms plants utilize to regulate their intake of CO2. Researchers say that their discoveries provide significant insights into the genetic mechanisms at cellular level, through which rising global emissions of CO2 will impact the world’s plant growth.