Effects Of Different Phosphorus-containing Passivators On Soil Microbial Communities In Cadmium-contaminated Farmlan

Phosphorus（P）-containing passivator is one type of common passivators in the remediation of agricultural soil contaminated with cadmium（Cd）in China.Previously,evaluation indicators of the remediation effect of heavy metal contamination in agricultural soils in China mainly include the soil available heavy metals concentration,heavy metals concentration in the edible parts of the crops and crop yield.There is a rare focus on the indicators of soil enzyme activity and microbial community.In the present study,Cd-contaminated agricultural soil to be safely used（SL）and strictly controlled（SE）were taken as the test soils,and three common P-containing passivators（hydroxyapatite（HAP）,calcium dihydrogen phosphate（MCP）and disodium hydrogen phosphate（DSP））were used as the test passivators.The effects of different P-containing passivators on the physicochemical properties,Cd fraction,enzyme activity,and microbial community diversity and structure in soil and its effect mechanism were analyzed and revealed.The results showed that（1）HAP and DSP had a good immobilizing effect on Cd in SL and SE,and the reduction rates of exchangeable Cd(Cd _Ex)in SL and SE were 31.0%（HAP）and 30.5%（DSP）,43.6%（HAP）and 57.0%（DSP）,respectively;MCP had a relatively poor immobilizing effect on Cd in SL and SE,and the reduction rates of Cd _Exin the SL and SE were 5.0%and 19.9%respectively;（2）HAP could promote and inhibit the enzyme activity in SL and SE,respectively;DSP could inhibit the enzyme activity in SL and SE;MCP could promote the enzyme activity in SL and SE;（3）after the application of the three passivators,the richness and diversity of the bacterial community in SL and SE were in the order of HAP>CK>MCP>DSP and CK>HAP>MCP>DSP,respectively;the application of HAP and MCP significantly decrease the diversity of fungal community in SE;（4）the application of HAP and DSP increased the relative abundance of Actinobacteria and Gemmatimonadetes in SL and SE,and the application of MCP increased the relative abundance of Rhizobiales in SE,which would improve the production and ecological environmental function of Cd-contaminated soil;（5）The main environmental factors affecting the bacterial community structure in SL and SE were acid phosphatase activity（contribution=42.4%,p<0.01）,available phosphorus concentration（contribution=12.4%,p<0.01）,residual Cd concentration（contribution=12.9%,p<0.05）of soil and soil available phosphorus concentration（contribution=44.6%,p<0.01）,available potassium concentration（contribution=17.0%,p<0.01）and p H（contribution=11.6%,p<0.01）of soil;The main environmental factor affecting the fungal community structure in SE is soil cation exchange capacity（contribution=23.1%,p<0.05）.From the perspective of the immobilizing effect of Cd and improvement of soil enzyme activity and microbial community,HAP is more suitable for the passivation remediation in SL,and DSP is more suitable for the risk controsl in SE.