Effects Of Elevated CO₂ On Transformation And Bioavailability Of Copper And Cadmium In Soil-wheat System

A hydroponic and a pot experiment with an open-top chamber (OTC) was conducted to investigate the effects of elevated CO₂ on soil copper and cadmium fractions and their bioaccumulation, soil microbial biomass carbon, dissolved organic carbon, the changes of pH and the content of the organic acids in root exudates in two contrasting wheat (Tritium aestivum L.) cultivars (cv. Ningmai No.8, a relatively heavy metal accumulating cultivar, and Linmai No.2, a relatively non-accumulating cultivar). The main results were presented as follows:With the elevation of CO₂, both shoot and root weight increased significantly, but the soil pH decreased. The shoot weight of Linmai No.2 and Ningmai No.8 in the treatment with elevated CO₂ (+300 ppm CO₂) increased by 36.9% and 25.2% respectively, and root weight by 55.1% and 59.7% respectively compared with the control. Both DOC and Cmic in wheat rhizosphere and non-rhizosphere varied with the elevation of CO₂. The DOC of Linmai No.2 and Ningmai N0.8 in the treatment with elevated CO2 increased at all stages. Under the condition of elevated CO2, the Cmic in Linmai No.2 rhizosphere and non-rhizosphere increased significantly. The Cmic in the soil grown with Ningmai No.8 differed with different stages. Furthermore, the microbial biomass quotient (qMB) increased to various degrees, and the qMB of Ningmai N0.8 was higher than that of Linmai No.2.With the elevation of CO₂, the content of the total organic acids in the two wheats' root exudates increased significantly. The total organic acids of Linmai No.2 (with the treatments of Cd5.0 and Cu2.5) increased by 21.7% and 36.2% respectively. And that of Ningmai N0.8 in the treatments of Cu5.0 and Cd10.0 increased by 24.6% and 22.1% respectively compared with the control. Among the main organic acids, the content of the...