Effects Of Elevated CO₂ On Growth, Zinc Accumulation Of Three Plants With Different Photosynthetic Pathways Under Zn Stress

With the development of society, a variety of man-made causes induces serious heavy metal pollution in soils, and bring about hazards to ecological environment. At present, little literature had reported combined effects of elevated CO2 concentration and heavy metal on plants.So, it is important to make a research on growth and development, heavy metal uptake and accumulation of plants while elevated CO2 under heavy metal stress, which can provide a reference for ecological security and phytoremediation. In this experiment, we studied the response of three plants with different photosynthetic pathways (C3 plant Lolium perenne, C4 plant Paspalum notatum and CAM plant Sedum alfredii) to elevated atmospheric CO2 which controlled by the use of open-top chamber (OTC), under the Zinc (Zn) pollution. Through analyizing the growth,the concentration of PCs,Cys and GSH in the shoot of plants, soil microbial biomass, Zn concentration and total Zn uptake of plants, the main conclutions could be drew as below:(1)The height, tillers, shoot and root dry weight of C3 plant Lolium perenne, C4 plant Paspalum notatum and CAM plant Sedum alfredii were increased at different levels because of elevated CO2, and the shoot and root biomass of Lolium perenne and Sedum alfredii were improved significantly. When CO2 was elevated, root/shoot ratios of three plants changed in different way.(2)The enrichment of CO2 significantly enhanced net photosynthesis (A), leaf internal CO2 (Ci), and water use efficiency (WUE) of Lolium perenne, Paspalum notatum and Sedum alfredii on both two different soils,while decreased Stomatal conductance (gst) of Lolium perenne and Paspalum notatum, but not very seriously. The soil pollution of Zn had little or no effect on A,Ci,WUE and gst of three plants.(3)On Zn contaminated soil, the root volume of Lolium perenne, length and tips of Paspalum notatum were sharply increased under elevated CO2, no matter on controlled soil or on Zn contaminated soil,elevated CO2 significantly enhanced length, surfer area, root volume, tips, forks of Sedum alfredii. Zn pollution obviously decreased root morphology parameters of Lolium perenne and Paspalum notatum, but root morphology parameters of Sedum alfredi decresed sharply only under atmospheric CO2.(4)No PCs were detected in shoots of three plants. On controlled soil, the concentrations of Cys in shoots of Lolium perenne and Sedum alfredii showed an obvious increase when elevated CO2.The concentration of GSH in shoot of Sedum alfredii increased a lot in response to CO2 enrichment. Under atmospheric CO2, Zn pollution sharply increased GSH in Lolium perenne and Sedum alfredii; while under elevated CO2, Zn pollution significantly increased GSH concentration in the shoot of Sedum alfredii.(5)Elevated CO2 obviously increased microbial biomass C in the soil of Lolium perenne, and also increased microbial biomass N in the soils of Paspalum notatum and Sedum alfredii, but not significantly.(6)Zn concentrations in the shoots and roots of Lolium perenne,Paspalum notatum and Sedum alfredii were declined under elevated CO2 concentration. However, under Zn polluted soil, elevated CO2 somewhat increased Zn concentration in shoot and root of Sedum alfredii. Elevated CO2 visibly enhanced total Zn uptake in the shoots of Lolium perenne and Sedum alfredii. On Zn polluted soil, obvious increase of Zn accumulation found in the roots of Lolium perenne while inhanced CO2 concentration. Elevated CO2 significantly increased root Zn accumulation of Sedum alfredii on two soils, but this increase was quite small of Paspalum notatum. Compared with controlled soil, Zn pollution significantly increased Zn concentrations and total Zn uptakes in the shoots and roots of three plants.The results demonstrated that elevated CO2 increased net photosynthesis rate, enchanced water use efficiency, promoted root growth, changed soil microbial biomass, and finally increased biomass of three plants.Lolium perenne, Paspalum notatum and Sedum alfredii all showed high tolerance to Zn pollution, elevated CO2 increased total Zn uptake, in which Lolium perenne and Sedum alfredii significantly increased. Therefore, integrating CO2 enrichment with Lolium perenne,Sedum alfredii could be a big advantage to enhance the efficiency of phytoremediation of Zn from soil.