| Guangxi is a typical secondary-enriched heavy metal pollution area with high geological background.Heavy metal pollution has greatly affected the soil quality and agricultural products grown in this area,and even threatened human health.The enrichment,migration and transformation of heavy metals in the high geological background area are quite different from the well-known laws of man-made heavy metal pollution.It is urgent to clarify the characteristics of heavy metal absorption and accumulation of agricultural products in the high geological background soil and the prevention and control of heavy metal pollution in the high geological background.Therefore,this paper takes the secondary enrichment type geologically high background heavy metal typical area-Heng County of Nanning City in Guangxi Province and part of the soil in Liuzhou City of Liuzhou City in Guangxi Province as the object to analyze the characteristics and influencing factors of soil microbial community changes,and take rice as the main body to carry out the soil-Study on the migration and accumulation characteristics and main controlling factors of heavy metals in the rice system.Factor research.Based on the factors affecting the accumulation of heavy metals in rice,the internal factors are the rice itself and the external factors are the characteristics of the soil environment.In this study,two different rice varieties and different soils were selected to carry out the research.The specifics are as follows: First,analyze the soil Cd in different geological and high backgrounds.Pollution characteristics and differences in microbial community structure;secondly,select two different parent material and high geological background soils,plant seven different rice varieties,analyze the heavy metal accumulation characteristics and main controlling factors of rice;finally select nine Cd content and p H There is a certain gradient of high geological background soil and two rice varieties with different Cd accumulation.The main control factors of heavy metal accumulation in rice are compared and the ecological risk assessment of heavy metal pollution in soil and rice is carried out.The main research results are as follows:(1)Fifteen high geologically background soils with secondary enrichment were selected in Heng county of Nanning city,and Liujiang District of Liuzhou City,Guangxi Province to analyze the difference in soil microbial community structure,and the main influencing factors were obtained by measuring soil physical and chemical properties,the total amount and availability of heavy metal Cd.The results showed that:(1)The content of available cadmium extracted by EDTA(Cd-EDTA)was higher than that of available cadmium extracted by Ca Cl2(Cd-Ca Cl2).There was a linear correlation between Cd-EDTA and total Cd content(R2=0.66).Cd-EDTA was negatively correlated with bacterial microbial diversity and positively correlated with fungal diversity,while Cd-Ca Cl2 showed the opposite result.(2)The copy numbers of soil bacteria are all higher than those of fungi,and there are significant differences in bacterial communities in different soils,while the differences in fungal communities are not obvious.(3)Redundant analysis results showed that the soil p H,SOM,T-Cd and Cd-EDTA affected soil bacterial composition,and soil p H contributed with the highest rate,which was 56.4%;soil T-Cd,SOM,AP,NH4+-N,p H,Cd-EDTA and NO3--N affected the fungal community,and T-Cd contributed with the highest rate of24.5 %.(4)Correlation analysis results showed that: p H,SOM and T-Cd were negatively correlated with the richness and diversity of bacteria in soil,and positively correlated with fungi.Besides,Cd-Ca Cl2 was negatively correlated with the species and richness of fungi.(2)The cadmium(Cd)accumulation characteristics of seven rice varieties(Ningliangyou 1,Y Liangyou 1,Shenliangyou,Tailiangyou,Yuejingsimiao,Youzhanbahao,and Huang Huazhan)were studied by pot-culture experiment in two paddy soils(Maling,Yunbiao)with different high geological backgrounds,and possible impacting factors were explored.The results showed that:(1)The grain Cd contents of the seven rice varieties grown in the two soils did not exceed the national food safety standard(GB 2762-2017),and the grain cadmium content of Shengliangyou was the lowest;(2)The grain Cd content of the seven rice varieties planted in the soil of Maling was higher than those of Yunbiao;(3)Redundancy analysis showed that the accumulation of Cd in grains were influenced by the plant height,the surface area of root,total cadmium in the soil,the EC and Eh of the soil during the heading stage.The correlation analysis showed that the main impacting factor of the grain Cd accumulation was different.In Maling soil,grain Cd content was mainly related to the rice root length,while it was related to the rice aboveground biomass in Yunbiao soil.(3)The high geological background soils with p H and Cd content gradients of nine soils(Dengwei Pengtang,Huilong,Lianghe,Longping,Qinlu,Simen,Nanan,Yulong)was selected to potted of high and low Cd accumulation varieties(Shenliangyou and Tailiangyou),analysis of rice Influencing factors of Cd accumulation,a rice Cd accumulation prediction model was established,and the results showed that:(1)Shengliangyou rice grown in different Nanan and Yulong soils is standard for Cd content in rice(GB 2762-2017),while those grown in Longping,Qinlu,Simen and Nanan soils The Cd content of T rice exceeds the standard;the Cd content of two kinds of rice rice planted in Pengtang soil is the lowest.(2)The Cd absorption and accumulation capacity of different parts from large to small are:root>stalk>husk(rice);(3)SOM and TF husk in soil-There is a significant positive correlation between rice and a significant negative relationship with BCF;(4)The Cd content of rice has the greatest correlation with soil Cd-EDTA,and the accumulation coefficient of rice Cd has a linear relationship with Cd-EDTA and T Cu content.In summary,under the geologically high background soil,the main factors affecting the distribution of microorganisms are soil p H,SOM and T-Cd content,and the main factors affecting the accumulation of Cd in rice are the soil Cd-EDTA and TCu content. |
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