Evaluating the Effects of Elevated CO2 on the Competition Ability between Various C3 and C4 Crops and Weeds in Greenhouse Condition

Since agriculture is both the source and sink of greenhouse gases, and plants show different responses to the elevated CO2 concentration, an experiment was conducted in 2006 at the research greenhouse of the faculty of agriculture of Ferdowsi University of Mashhad. The purpose of the experiment was to examine the effects of elevated CO2 on the competition ability between various crops and weeds in factorial arrangement within a completely randomized design with three replications. The factors included ambient (360ppm) CO2 and elevated (700 ppm) CO2 concentrations and various combinations of the plantation of crops (millet and soybean) and weeds (pigweed and lambsquarters) of C3 and C4 species, whether of the pure culture or intercropping. The results of the experiment showed that, as the CO2 concentration increased, the leaf area and root dry weight of millet increased whereas those of other species decreased. Millet,s root length increased whereas those of other species decreased. Root dry weight in each cultural combinations, compared to the ambient CO2 concentration, decreased. The amount of chlorophyll in lambsquarters, increased whereas it decreased in pigweed, millet and soybean.