The Effect Of Elevated CO₂ On Growth And Copper Concentration Of Seven C₃ Herbage Grass Species

Along with the deteriorating quality of living environment, the heavy metal pollution brought enormous losses to environment and economy, and posed a huge threat to the steadily sustainable development of agricultural production and human health, thus public concern about soil pollution by heavy metal had grown in recent years, especially copper pollution. Phytoremediation had several advantages over other chemical and physical remediation methods, such as the in-situ management process (small disturbance to the soil environment), low-cost treatment, generally no secondary pollution, landscaping and even the recovery of heavy metals. However, there was also some limitation, for instance, the low biomass and slow growth of hyperaccumulator, the difficulty of conducting the mechanized operation, so a bottleneck problem that needed to be tackled in the future is how to increase the absolute absorption of heavy metals in order to enhance the efficiency of phytoremediation, or by improving the plant's biological characteristics (growth rate, growth cycle, etc.) to increase absorption and total accumulation of heavy metal per unit area on the plant so as to elevate the relative efficiency of phytoremediation. Meanwhile, due to the impact of human activities, mainly coal, oil and other fossil fuel burning, which aggravated the greenhouse gases - particularly CO₂- emission, the atmospheric [CO₂] gradually increased. Elevated atmospheric [CO₂] could increase plant biomass and production and alleviate the poisoning effect of heavy metals, etc. Literature search showed that there are abundant research about the effect of elevated [CO₂] on crops (especially herbage) biomass and yield, but scarce about the effect of elevated [CO₂] on heavy metal accumulation in their stress condition. With the development of livestock industry and environmental pollution extending from the local to the whole, increasing attention should be paid to the health quality of pasture, especially for the impact of heavy metals on the growth and health quality of pasture, but this study is also scarce. In this paper, we used the open-top chamber (OTC) to investigate the effect of elevated [CO₂] on the growth and copper accumulation of seven C₃ herbage grass species-red clover (Trifolium Pratente L.), alfalfa (Medicago sativa L.), Indian lettuce (Lactuca indica L.), rumex (Rumex patientia×R. Tianschanicus cv. Rumex-K1), annual ryegrass (Lolium multiflorum Lam.), perennial ryegrass (Lolium perenne L.), wintergrazer (Secale Cereale L. cv. Wintergrazer-70). The main results were as follows:1. The effect of elevated [CO₂] on the growth of seven C₃ herbage grass speciesElevated [CO₂] (approximately 860μmol/mol) significantly increased plant height on average by 41% ranged from 7%～221% (P＜0.001); Elevated [CO₂] (approximately 860μL/L) significantly increased shoot dry weight by 30% ranged from -1%～55% (P＜0.001); Elevated [CO₂] (approximately 860μL/L) significantly increased root dry weight by 17% ranged from -37%～45% (P＜0.001); Elevated [CO₂] (approximately 860μL/L) significantly increased shoot/root by 16% ranged from-22%～111%2. The effect of elevated [CO₂] on the pH value of rhizospheric soil of seven C₃ herbage grass speciesElevated [CO₂] (approximately 860μmol/mol) significantly reduced pH value of rhizospheric soil on average by 0.28 unit ranged from 0.24～0.43 unit(P＜0.001).3. The effect of elevated [CO₂] on the copper concentration of seven C₃ herbage grass speciesElevated [CO₂] (approximately 860μmol/mol) did not have significant impact on copper concentrations of herbage shoot (P=0.934), and increase the Cu concentration of herbage shoot on average by 1% ranged from -33%～39%; Elevated [CO₂] (approximately 860μL/L) significantly increased the Cu concentration of herbage root on average by 17% ranged from -12%⁵0%(P＜0.001).The results of the study showed that, elevated [CO₂] significantly increased herbage biomass, and the shoot/root ratio of DM also increased with the elevation of [CO₂], which suggested that the shoot grew much faster than root for most herbage under the elevation of [CO₂]. Moreover, elevated [CO₂] significantly reduced the pH value of rhizospheric soil and increased root copper concentration, but did not have significant impact on shoot copper concentration. Therefore, if the poultry were fed by the aboveground of herbage and based on recommendation that the diet of cow must be below the 10mg Cu per kg DM set by the NRC(2001), elevated [CO₂] could intensify or alleviate the healthy risk issue of different C₃ herbage grass species under two copper concentration soil. The findings of the study could provide the experimental data for comprehensive management of soil contaminated by copper and the crop safety assessment.