The potential and mechanism of cadmium reduction in tillering rice by raising seedlings with different manganese rich substrates
The problem of cadmium(Cd)in rice exceeding the standard in China is relatively serious,and the cultivation of manganese(Mn)rich seedlings has the potential to reduce the absorption of Cd by rice,but at present there is a lack of mature Mn-rich seedling breeding substrate.This study used peat(N),vermiculite(Z),coconut bran(Y),yellow-mud(H),organic fertilizer(F),and rice husk biochar(D)as substrate materials to prepare 8 kinds of Mn-rich substrates with different raw material ratios.Conventional substrate(60%peat+20%coconut bran+20%vermiculite,60N20Y20Z)were used as the control to compare the physical and chemical properties of the substrates,seedling growth and Mn content,as well as the absorption and transportation of Cd in rice after transplantation were studied,and the Cd reduction potential in rice and related factors of Mn-rich substrates were explored.The results showed that the Mn concentration in Mn-rich substrates increased by 1.07-2.38 times compared to the control(369 mg·kg-1),ranging from 764-1247 mg·kg-1.The Mn concentration in the substrates was significantly negatively correlated with the bulk density,and was not significantly related to other physicochemical parameters.The Mn-rich substrates without yellow-mud significantly inhibited the growth of seedlings,and the dry weight of plant roots and shoots decreased by 23.8%-50.1%and 15.8%-39.2%,respectively,compared to the control.However,the Mn-rich substrates containing yellow-mud did not affect rice growth,and even benefited to rice growth.The Mn absorption efficiency of seedlings in Mn-rich substrates containing yellow-mud was 0.15-3.74 times higher than that of the control,and the higher the proportion of yellow-mud,the greater the Mn absorption efficiency.On the contrary,a Mn-rich substrate without yellow-mud was not conducive to the absorption of Mn by seedlings.Therefore,the Mn-rich substrate containing 40%peat,20%coconut bran,20%vermiculite,and 20%yellow-mud(40N20Y20Z20H)resulted in the highest Mn concentration in the roots and shoots of seedlings.After transplanting,the Mn-rich seedlings in 40N20Y20Z20H treatment reduced Cd concentrations in the root and shoot of rice by 16.0%and 39.6%at the tillering stage,respectively,and the translocation factor of Cd from the root to the shoot was decreased by 27.5%.Mn-rich substrate of 40N20Y20Z20H combined with basal lime application further reduced Cd concentration of tillering rice shoots by 65.8%.The structural equation model(SEM)results showed that the Mn concentration in rice roots inhibited the absorption and transport of Cd in the roots,thereby affecting Cd accumulation in rice shoots.Therefore,the Mn-rich substrate of 40N20Y20Z20H has the potential on promoting rice growth and reducing Cd absorption in field application.
soil Cd pollutionseedling raising substratemanganese enrichmenttransportrice
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