| Magnesium(Mg)is a medium.amount of nutrients needed by plants.In rice-soil system,Mg has a certain influence on mobility of Cd in soil and Cd transport in rice.Using Mg to regulate Cd pollution in paddy soils and Cd uptake and transport in rice provides new ideas for the treatment of soil Cd pollution and safe production in rice fields.There are many opinions about the effects of Mg on soil Cd activity and the ability to transport Cd to plants.Some scholars believed that application of exogenous Mg effectively reduced the activity of Cd in soil,reduced the absorption of Cd by spinach,and increased the yield of spinach.There were also some studies that Mg not only increased the corn yield,but also increased the accumulation of Cd in corn,increased the ability of transport Cd in the aboveground.In this study,pot experiments were conducted to investigate the soil physicochemical properties and Cd bioavailability in soils with mild(L,Cd=0.5 mg·kg-1)and moderate(M,Cd=1.5 mg·kg-1)Cd contamination with different amounts of exogenous Mg,to study the effects of Cd uptake and translocation in rice varieties(XWX-12)and Weiyou 46(WY-46),and to explore the factors influencing rice yield and Cd contents in brown rice.The main findings are as follows:(1)Application of exogenous Mg to XWX-12 and WY-46 planting soils resulted in significantly lower soil pH values than the control at the two Cd contamination levels,and this effect decreased with prolonged rice growth seasons.Application of exogenous Mg had no obvious effects on soil CEC values.(2)Application of exogenous Mg had little effects on Cd contents of 0.01 mol·L-1 CaCl2 extraction(CaCl2-Cd)in L soil.Contents of CaCl2-Cd in M soil decreased with rice growth seasons,and were slightly higher compared with the control at rice maturity.Under the two Cd pollution levels,TCLP-Cd contents in the soils of the two rice varieties increased significantly at the mature stage.(3)Application of exogenous Mg80 and Mg320 significantly increased rice aboveground biomass and yield.In L soil,Mg treatments increased yields of XWX-12 and WY-46 by 16.6%、37.8%and 32.5%、38.2%,respectively,and in M soil by 33.1%、15.7%and 39.5%、69.1%,respectively.(4)Under the two Cd pollution levels,Mg treatments increased Cd contents in roots,stems and leaves,and husks of rice for the two cultivars to different extents,but Cd contents in brown rice decreased.Mg treatments significantly increased Cd transport coefficient from leaf to stems and reduced Cd transport coefficient from rice husk to brown rice in two rice varieties in two Cd pollution soils,reduced Cd contents in root during the rice early growth stages,but had no obvious effects on other parts of rice.Cd contents in brown rice at the mature stage of XWX-12 and WY-46 in L soil were slightly lower than those of the control,and the range was between 0.01 and 0.02 mg·kg-1.Cd contents in XWX-12 brown rice in M soil increased slightly.With increasing Mg application,Cd contents in XWX-12 brown rice showed a decreasing trend,ranging from 0.01 to 0.02 mg·kg-1,which was significantly lower than that of the control.Cd contents in WY-46 brown rice increased with increasing Mg application,the maximum was 0.09 mg·kg-1,which was significantly higher than the control,but still lower than the national food contaminant limit standard 0.2 mg·kg-1.(5)The results of RDA analysis showed that the main environment factors for rice biomass,yield,and Cd contents in brown rice were soil pH and contents of CaCl2-Mg and TCLP extraxted Mg(TCLP-Mg)for two rice varieties.Soil pH values were negatively correlated with Cd contents in brown rice;contents of CaCl2-Mg and TCLP-Mg were positively correlated with rice biomass and yield,but negatively correlated with Cd contents in brown rice.Soil environmental factors were able to explain 72.8%and 78.6%of changes in the rice biomass,yield and Cd contents in brown rice in XWX-12 and WY-46,respectively. |
