The impact of elevated CO 2 on growth and competitiveness of C 3 and C 4 crops and weeds Hamid

This experiment was conducted to evaluate the effects of normal CO2 level (350ppm) and elevated concentration (700ppm) on growth and competitive ability of millet and soybean against pigweed and lambsquaters. The plants were planted as mono and multicultural to study interand intra-specific competition in the greenhouse. Root and shoot dry weights and chlorophyll value was measured at the end of vegetative growth. The results showed that plant chlorophyll content rose up by increasing CO2 concentration, especially in C3 plants when they were intercropped with C4 plants. CO2 elevation caused considerably higher root, stem and leaf weight in C3 plants than in C4 plants. In intercropping condition, C4 plants shoot dry weights decreased under elevated CO2 concentration. It indicated that competitive ability of those plants reduced in these situations. In all investigated plants, root shoot ratio reduced by increasing CO2 concentration. Generally, PRY comparisons showed that competitive ability of soybean and lambsquarter increased and millet and pigweed decreased under elevated CO2 concentration. Therefore weed – crop interactions would be highly affected by CO2 concentration.