Effects Of Silicon On Physiological-Biochemical Properties And Heavy Metals Uptake Of Turfgrass Under Heavy Metals Compound Pollution

With the rapid development of industry and agriculture, there is a significant increase of chemical pollutants in ecosystems, which becomes a big challenge for global development and human health, especially for soil heavy metal contamination. How to control polluted soil and reduce the mobility of heavy metals in soil-plant system has become the focus.The research progress on heavy metal pollution in soil-plant system and the effects of silicon on plant growth and heavy metal uptake are reviewed in the paper. Ryegrass and tall fescue were selected for pot experiments with orthogonal experiment design L₉(3⁴) and L₁₆(4⁵) in the greenhouse to study the effects of silicon addition on physiological-biochemical properties and heavy metal uptake in soil-turfgrass system under the soil compound pollution of Cd, Zn and Pb.The results showed that:(1) Under the compound pollution, the biomass of ryegrass was significantly inhibted by increasing Cd application, 50 mg·kg^-1 Zn and Pb can facilitate the biomass accumulation, but both shoots and roots biomass were inhibited at 300 mg·kg^-1 Zn and 350 mg·kg^-1 Pb. Cadmium, Zn and Pb of the same concentration differently affected chlorophyll a, b and total content of chlorophyll for tall fescue and ryegrass. However, chlorophyll content of both turfgrass decreased when Cd application was higher than 1 mg·kg^-1, and Zn and Pb application higher than 50 mg·kg^-1. The sensitivity of these two kinds of turfgrass' chlorophyll to Cd, Zn and Pb were different: ryegrass was sensitive to Zn and 50 mg·kg^-1 Zn increased its chlorophyll content; 1 mg·kg^-1 Cd stimulated and increased chlorophyll content of tall fescue. Cadmium, Zn and Pb affected the CAT and POD activities of the turfgrass as well: ryegrass showed a positive response of CAT and POD at 1 mg·kg^-1 Cd; CAT activity was reduced if Zn application was higher than 50 mg·kg^-1, while both CAT and POD activities were increased if Pb application was higer than 50 mg·kg^-1. Compare with CAT, there was lag of POD to Zn concentration for ryegrass. The CAT activity of tall fescue was significantly inhibited with increasing Cd and Pb concentration but it had positive response to Zn. The POD activity increased with increasing Cd, Zn and Pb concentration. In addition, there was no significant effect of Cd, Zn and Pb on relative water content of tall fescue without regular rules in general. MDA accumulated significantly in tall fescue with increasing Cd, Zn and Pb in soil especially for Pb.(2) Effects of Si on biomass accumulation of ryegrass were very significant. By increasing chlorophyll content and reducing chlorophyll a/b in ryegrass, Si helped to improve capability of photosynthesis and slow down lamina senescence, but its concentration should be under control in the initial growth period of ryegrass. Although Si can slow down lamina senescence of tall fescue, there was no regulation to show its effect on chlorophyll content. Silicon stimulated CAT activity for both ryegrass and tall fescue, and kept POD activity at an appropriate level. Meanwhile Si increased lamina's relative water content and reduced MDA content of tall fescue significantly.(3) Obvious dose-effect was found for Cd, Zn and Pb uptake by the turfgrass. With increasing Si concentration, Cd, Zn and Pb uptake by ryegrass and tall fescue decreased gradually. There was a significant negative linear correlation between Si addition and Cd, Zn and Pb concentration in the turfgrass. With increasing Si addition, soil exchangeable and carbonate-bound Zn, Cd and Pb decreased, while Fe-Mn oxides and residual fraction increased gradually, and thus reduced heavy metal bioavailability and inhibited the mobility of heavy metals from soil to ryegrass. As for the variation, exchangeable Cd decreased most, followed by Zn and Pb. Tall fescue had stronger ability to take up Cd, Zn and Pb than ryegrass.In a word, Si has a good potential to control soil heavy metal pollution. Silicon addition to some kinds of turfgrass with strong ecological adaptability could be a new option to control heavy metal pollution in soil-plant system.