Effect Of Sulfur On The Bioavailabilitv Of Cadmium And Characteristics Of Rhizosphere Bacterial Community In Rice-sedum Alfreddii Hance Rotation System

It's of great significance to explore and optimaze the technical model of phytoremediation coupled with agro-production for the remediation and utilization of large areas of cadmium(Cd)contaminated soil in China.As an important agronomic measure,the regulation mechanism of sulfur fertilizer application on the bioavaiability of Cd in soil are not entirely clear.To better understand the effects of two forms of sulfur fertilizers(S0 and Na2SO4)on the bioavailability of Cd and the rhizosphere bacteria community in the rotation system of rice(Oryza sativa L.)-Sedum alfredii Hance,combination of inductively coupled plasma mass spectrometry(ICP-MS),high performance ion chromatography(HPIC)and 16S rRNA gene sequencing was applied to investigate the key taxa associated with transformation of sulfur and plant absorption of Cd.The research provided the optimized model for the process of phytoremediation coupled with agro-production.The main results incude:1.The different effects of sulfur fertilizers(S0 and Na2SO4)on the bioavailability of Cd in soil and rhizosphere bacteria community of rice under two ways of water management were demonstrated.The results showed that under continuous flooding(CF)condition,the application of sulfur fertilizers reduced the Cd bioavailability in the way of promoting the formation of metal sulfide and increasing the pH of soil.Conversely,the availability of Cd in soil was increased after the addition of sulfur fertilizer under dry and flooding cycle(DFC),owing to the sulfur oxidation and the decreased pH of soil caused by the fluctuation of soil redox state in this condition.In addition,sulfur fertilizers stimulated the enrichment of large number of sulfur-reducing bacteria in the rhizosphere of rice plants under CF condition,whereas promoted the specific colonization of bacteria related to sulfur oxidation and growth promotion in DFC condition.The above results indicated that the additon of sulfur fertilizers impelled the shaping of unique rhizosphere bacterial commuunity under the mode of continuous flooding(CF),which could promoted the growth of rice and safe production by reducing the bioavailability of Cd in soil.2.The influence of sulfur application on the Cd extraction and rhizosphere bacteria community of S.alfredii in later rotation were investigated.The results demonstrated a promotion effect of sulfur fertilizers on the growth and Cd uptake of S.alfredii,in the way of impelling oxidation of more sulfides,this transform of sulfur speciation will decrease the pH of soil,and further result to the increase Cd biovailability.Several key taxa related to sulfur oxidation,which will promote growth and metal activation,were especially abundant in rhizosphere of S.alfredii after the application of sulfur fertilizers.Several genes involved in sulfur metabolism and amino metabolism related to heavy metal detoxification and tolerance in the rhizosphere of S.alfredii were also identified after fertilizer treatments.The above results suggested that the interations of Sulfur application and Sedum alfredii planting together shaped the specific rhizosphere bacterial community,which involved in sulfur oxidation,plant growth promotion or metal mobilization.