Diurnal Light Regulates The Rhizosphere Microbial Composition And The Mechanism Of Transformation Of Arsenic Morphology In Rice

Arsenic,a highly toxic metalloid widely found in nature,is internationally recognized as one of the Class I carcinogens that can enter the food chain posing a threat to human health.Rice,a major human food crop,is more likely to accumulate arsenic in the body than other crops due to its long-term growth in flooded conditions.The chemical morphological transformation of soil arsenic mediated by rhizosphere microorganisms determines its mode and ability to enter the rice body.In addition,light,as an upstream factor,affects the rhizosphere environment and changes the composition of rice rhizosphere microbial community during the diurnal cycle.However,there is still a lack of research on the mechanism of microbial assembly in response to the changes of the rhizosphere environment and the transformation of arsenic morphology in the rhizosphere under diurnal variation.Therefore,in this study,by setting up bacterial and sterile control groups with arsenic treatment,we used rice as the research object to investigate the mechanism of rhizosphere microorganisms assembly regulated by light and dark conditions on the transformation of arsenic morphology.The main findings were as follows:(1)Diurnal light regulation affects the rhizosphere microenvironment.Compared with the non-rhizosphere,the p H and DO content of rhizosphere solutions decreased due to root secretion,with higher under light conditions and lower under dark conditions,exhibiting an overall wave-like fluctuation.In addition,the morphology of arsenic differed between light and dark conditions,with the proportion of As(V)increasing under light conditions.In the sterile system,the proportion of As(V)was 7.5%higher under light condition than under dark condition;in the bacterial system,the proportion of As(V)was 1.67% higher under light condition than under dark condition.(2)Changes in the rhizosphere microenvironment affect the assembly process of rhizosphere microbial community.Compared with non-rhizosphere,the rhizosphere environment was relatively enriched in Alpha-and Gammaproteobacteria,which may be related to the increase in the relative proportion of homogenizing dispersal influenced by the increase in organic matter content.In addition,the assembly process of rhizosphere microorganisms was influenced by diurnal light regulation,with heterogeneous selection and homogenizing dispersal dominating the assembly of rhizosphere microorganisms under light conditions,while the relative importance of homogeneous selection and homogenizing dispersal increased under dark conditions.(3)Diurnal light regulation affects the composition of rhizosphere microbial communities.Under light conditions,Pseudomonadales,Xanthomonadales,Bacillales,Rhizobiales,Micrococcales and Burkholderiales were significantly enriched in rhizosphere compartment.Under dark conditions,Erysipelotrichales,Sphingomonadales,Burkholderiales,Hydrogenophilales and Enterobacteriales were significantly enriched in rhizosphere compartment.Notably,these taxonomic groups were potentially involved in nitrogen fixation,phosphorus solubilization and the process of arsenic morphological transformation.(4)Diurnal light regulation affects the functional composition of rhizosphere microorganisms.The abundance of microbial functions related to arsenic oxidation,nitrite conversion(oxidation,reduction,and ammoniation)and some carbon metabolism were significant higher under light conditions;while the relative abundance of microbial functions related to denitrification,oxidation of nitrogen,sulfur oxide compounds,and hydrocarbon degradation were relatively higher under dark conditions.In addition,functional pathways associated with arsenic metabolism are increased or decreased in the rhizosphere by diurnal light regulation,which may affect the process of arsenic morphological transformation.(5)According to CCA analysis,p H,As(V)and MMA were the environmental factors for the difference in rhizosphere microbial composition between light and dark in the arsenic treatment group;p H,DO and succinate acid were the environmental factors for the difference in rhizosphere microbial composition in the arsenic-free treatment group.These environmental factors were consistent with the influence factors driving the functional composition of microorganisms.Arsenic metabolism functions were significantly correlated with p H,DO and organic acids,which may be due to differences in the composition of rhizosphere microorganisms regulated by light.In this study,through comparative analysis of the characteristics of changes in the rhizosphere microenvironment caused by diurnal light regulation,we explored the differences in the assembly mode and functional composition of rhizosphere microorganisms under diurnal variation,and revealed the mechanism of the rhizosphere microbial mediated arsenic morphological transformation.This study may provide new insight of the rhizosphere microbial assembly process under diurnal light regulation,and improve our understanding of the rhizosphere microbial mediated arsenic morphological transformation process under light regulation.