Effect Of Cotton Stalk Biochar On Cadmium Migration And Soil Microbial Community Structure In Soil-Rice System

To investigate the effect of cotton stalk biochar on retarding the stress of cadmium on the growth of rice(Oryza sativa L.),an outdoor pot experiment was conducted with Tefengyou 2 rice as test material.Adding cotton stalk biochar with 0%,1%,2.5%and 5%in the paddy soil with cadmium concentration of 0,1,4 and 8 mg·kg-1.The effects of application of biochar on plant height,leaf SPAD value,photosynthetic characteristics,leaf water use efficiency and other physiological and yield indexes were analyzed in rice jointing stage,booting stage,filling stage and ripening stage.After rice harvest,the effects of different concentrations of cotton stalk biochar on alkaline soil physical and chemical properties,cadmium enrichment and transfer in rice and the occurrence of cadmium in soil were analyzed under different concentrations of cadmium stress.To analyze the influence of cotton straw biochar on the diversity and structure of rice rhizosphere soil bacterial community under cadmium stress,reveal the potential function of the bacterial community,and explore the relationship between soil environmental factors and bacterial community structure.To analyze the effects of cotton stalk biochar and cadmium stress on the diversity,structure abundance and function of rhizosphere soil fungi,and to explore the correlation between soil environmental factors and fungal communities under the control of stalk biochar.(1)Application of cotton stalk biochar can significantly increase the nutrient content in cadmium-contaminated soil.Cadmium pollution treatment significantly inhibited rice plant height,leaf SPAD value,photosynthetic capacity,leaf water use efficiency and yield(P<0.05).The application of 1%cotton stalk char can significantly increase rice plant height,leaf water use efficiency and yield under cadmium pollution treatment;the application of 2.5%cotton stalk biochar can significantly improve rice photosynthetic capacity;the SPAD value of rice leaves increased significantly with the increase of cotton stalk carbon application(P<0.05)(2)The application of cotton stalk biochar significantly reduced the cadmium content in rice soil and various organs of the rice,and the application of 5%cotton stalk biochar could reduce the cadmium content of brown rice exceeding the standard in the Cd4 and Cd8 concentrations to the national standard range.Cotton stalk biochar treatment reduced the content of available cadmium(reducible and oxidizable)in the soil and weakened the cadmium enrichment-transport capacity(P<0.05).Soil pH,electrical conductivity,and nutrient indicators have extremely significant negative correlations with cadmium content in rice and weakly acid-extracted,reducible,and oxidizable cadmium content in the soil,and have a positive correlation with residual cadmium content(P<0.05).(3)Cadmium pollution and cotton stalk biochar treatment significantly affected the ?-diversity and structural composition of rice rhizosphere soil microorganisms.In cadmium-contaminated soil,the application of cotton stalk charcoal could significantly increase the richness and ?-diversity of bacterial communities,but significantly reduce the ?-diversity of fungal communities in each cadmium-contaminated soil.Proteobacteria,Chloroflexi,Acidobacteria,and Gemmatimonadetes are the dominant bacteria in rice rhizosphere soil.Ascomycota,Aphelidiomycota and Chytridiomycota are the dominant fungi in the rhizosphere soil of rice.Cotton stalk biochar increased the relative abundance of Proteobacteria and Actinomycota,but decreased the relative abundance of Phytophthora.Soil available potassium,organic matter,oxidizable cadmium,reducible cadmium,and available phosphorus have the greatest effect on the structure of microbial community in the rhizosphere of rice.