Global warming could increase rice, soybean and wheat production in some areas, but the greater plant growth could also hurt the nutritional value of the crops. The nutritional quality declines because while the plants produce more seeds with higher levels of carbon dioxide, the seeds themselves contain less nitrogen. Research has shown that individual crops vary in their response to higher carbon dioxide levels. Rice is the most responsive with its seed production increasing an average of 42 percent. Soybeans show a 20 percent increase in seed, followed by wheat with 15 percent and corn with 5 percent. Even though seed size increases, the amount of nitrogen in the seeds falls by an average of 14 percent across all plants except cultivated legumes, such as peas and soybeans. Nitrogen is important for building protein in humans and animals. If anything, plant biologists want to boost the levels of nitrogen in crops.