| With the continuous development of industry and agriculture,the problem of Cd contamination in paddy soil-rice system has been aggravated worldwide.It is important to take effective measures to reduce the effectiveness of Cd in paddy soils and to reduce the excessive Cd content in rice.As one of the most commonly used chemical fertilizers in rice production,phosphate fertilizer plays an important role in rice production.The reasonable application of phosphate fertilizer can reduce the Cd effectiveness of paddy soils and thus reduce the Cd uptake and accumulation in rice,which has played an important practical significance in regulating the Cd uptake and accumulation in rice.In this study,we compared the effects of three phosphate fertilizers,namely calcium superphosphate（widely and commonly applied in agricultural production and used as a control in this paper）,monoammonium phosphate（ammonium dihydrogen phosphate,ADP）and calcium-magnesium phosphate（calcium magnesium phosphate,CMP）,on the basic physicochemical properties（p H,CEC,DOC,etc.）,Cd effectiveness and Cd fugacity of rice soils,and Cd content in various parts of the rice plant in multiple consecutive seasons.The effects of three phosphorus fertilizers on Cd migration and transformation in the soil-rice system were clarified,and the mechanisms of phosphorus fertilizer regulation of Cd migration and transformation in the soil-rice system were discussed in the context of root surface gel film formation and its Cd fixation,Cd subcellular distribution and antioxidant system in roots and flag leaves,and transcriptional genomics.The main findings are as follows.（1）Compared with the control（calcium superphosphate）,the soil DOC and fast-acting phosphorus contents decreased by 1.02～16.94%and 6.77～17.95%,5.05～18.41%and 10.87～50.77%,respectively,and the soil DTPA-Cd contents increased by 9.03～17.10%and 1.35～14.14%,respectively,in the ADP and CMP treatments,with no significant effects on soil p H and CEC contents.Soil Cd was dominated by the acid-extracted and residue states,with the sum of the two accounts ranging from 70.52%～89.20%.Compared with CK,the percentage of acid-extracted Cd in ADP and CMP treatment decreased by 1.44～8.17%and 2.27～4.41%,and the percentage of reducible Cd increased by 0.30～2.84%and 0.24～1.19%,and the percentage of reducible and residual Cd increased by 0.19～0.65%and 0.32～0.70%,0.23～4.98%and 1.11～3.47%,respectively,with decreasing overall activity.（2）Both monoammonium phosphate and calcium-magnesium phosphate fertilizers reduced Cd content in all organs of rice plants to some extent.Compared with CK,ADP and CMP treatments reduced rice Cd and root Cd contents by 7.24-35.89%and 6.28-32.77%,16.01-47.01%and 11.16-20.24%,respectively,and rice BCF by 5.44-45.80%and 1.53-25.21%,respectively.Root Cd content showed a highly significant positive linear relationship with DTPA-Cd（r=0.680**）;brown rice Cd content showed a highly significant positive linear relationship with root Cd content（r=0.772**）,and rice Cd content was indirectly constrained by DTPA-Cd.（3）Both monoammonium phosphate and calcium-magnesium phosphate fertilizers had a role in increasing the antioxidant enzymes and glutathione content,with calcium-magnesium phosphate fertilizer being more effective than monoammonium phosphate.Compared with CK,the cell wall Cd content of the first node in ADP and CMP treatment increased significantly by 19.47%and 48.03%,respectively;the cell wall Cd content of the flag leaf in CMP treatment increased by 14.47%,and monoammonium phosphate and calcium-magnesium phosphate fertilizer had a certain effect on cell wall fixation of Cd.The superoxide dismutase（SOD）,peroxidase（POD）,and reduced Glutathionease（GSH）contents were significantly increased by 140.07%and 265.20%,59.51%and 58.10%,46.50%and 91.76%,respectively.（4）The optimal reduction in Cd content of monoammonium phosphate rice was the combined effect of increased Os HMA3 expression,reduced root Cd content and decreased transport coefficient.mn and Ca were the two elements that affected rice plants with higher Cd content in this paper and reflected antagonistic relationships mainly in the roots,with a significant negative linear relationship between root Mn and root Cd（r=-786*）and a significant positive relationship between root Cd and root Ca（r=0.718*）,contributing to the reduction of Cd accumulation in the roots.Compared with CK,TF flagleaf/other stem leaf and TF husk/spike axis were reduced by 27.78%and 38.89%,17.31%and17.32%,respectively.root and flag leaf Os HMA3 gene expression were significantly increased by 29.23%and 23.85%,305.36%and 119.09%by ADP and CMP treatments,respectively.both monoammonium phosphate and calcium-magnesium phosphate fertilizers caused Os HMA3 gene overexpression as well as reduced Cd transfer from other stems and leaves（including the first node）and flag leaves to the seeds. |
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