Carbon Dioxide Reduces Crop Yields
December 1, 2012

Crop Yields May Be Lessened Due To Carbon Dioxide

April Flowers for — Your Universe Online

Atmospheric carbon dioxide content continues its climb, heating up the climate. For plants, however, the gas is a necessary part of their survival. It provides the carbon needed to produce glucose and other important substances, leading scientists to question if more carbon dioxide is better.

The answer isn't as simple as that, unfortunately. The plants used for our most basic food supply today have not been bred for vertical growth. Rather, they were bred for short stalks and a high yield of grains. A new study from the Max Planck Institute of Molecular Plant Physiology and the University of Potsdam reveals that an increase in carbon dioxide levels could cancel out the beneficial effects of dwarf varieties of food crops.

In the 1960s, a variety of rice called IR8 — which has virtually disappeared from the market today — caused quite a stir. IR8 is a dwarf variety of rice that produced incredible yields and warded off the food shortages scientists had predicted at the time. Most other high-yield varieties buckled under the weight of their grains, but IR8's strong short stalks supported the weight of its high yield grain without a problem.

Additionally, through the lack of vertical growth the plant saved on nutrients and energy, making it even more productive. Every bit of energy and nutrition not needed for longer stalk growth was available to the grains. Plants like IR8 were hailed as part of the "Green Revolution" in agriculture and protected humanity against global famine.

Since the 1960s, however, IR8 yields have declined by about 15 percent, making the cultivation of this once promising plant seem as no longer worthwhile. It is necessary to understand the mechanism behind dwarf growth in plants to understand why IR8 has declined in yield and popularity.

The production of the plant growth hormone gibberellic acid depends upon an enzyme that the dwarf variety of rice lacks. Without gibberellic acid, vertical stalk growth is retarded while still allowing for strong stalks and high-yield grains. Nothing has changed in the genetic makeup of IR8 in the last fifty years, however, it continues to decline in yield. Because the plant has remained the same, the research team wanted to find out whether this decline was possibly linked with the global increase in atmospheric carbon dioxide levels, as the current concentration is 25 percent higher than in the 1960s.

The team chose the model plant Arabidopsis thaliana — thale cress. They observed that a higher carbon dioxide concentration unblocked the capacity of the dwarf variety to form gibberellic acid, thus triggering a growth-stimulating effect. The dwarf plants gradually lost their advantage, coming to increasingly resemble the control plants.

“Breeders now face the challenge of developing new plants that can continue to provide good yields under the altered climatic conditions,” says Jos Schippers.

Farmers prefer short-stalked varieties of wheat as well as rice. Both cereal grains are staple foods consumed by a majority of the global population.

The team is continuing their research, looking for the mechanism through which carbon dioxide influences the growth of the plants.