Nitrogen application and intercropping change microbial community diversity and physicochemical characteristics in mulberry and alfalfa rhizosphere soil

Intercropping of mulberry(Morus alba L.)and alfalfa(Medicago sativa L.)is a new forestry-grass compound model in China,which can provide high forage yields with high protein.Nitrogen application is one of the important factors determining the production and quality of this system.To elucidate the advantages of intercropping and nitrogen application,we analyzed the changes of physicochemical properties,enzyme activities,and microbial communities in the rhizosphere soil.We used principal components analysis(PCA)and redundancy discriminators analysis to clarify the relationships among treatments and between treatments and environmental factors,respectively.The results showed that nitrogen application significantly increased pH value,available nitrogen content,soil water content(SWC),and urea(URE)activity in rhizosphere soil of monoculture mulberry.In contrast,intercropping and intercropping+N significantly decreased pH and SWC in mulberry treatments.Nitrogen,intercropping and intercropping+N sharply reduced soil organic matter content and SWC in alfalfa treatments.Nitrogen,intercropping,and intercropping+N increased the values of McIntosh diversity(U),Simpson diversity(D),and Shannon-Weaver diversity(H’)in mulberry treatments.However,PC A scatter plots showed clustering of monoculture mulberry with nitrogen(MNE)and intercropping mulberry without nitrogen(M0).Intercropping reduced both H’and D but nitrogen application showed no effect on diversity of microbial communities in alfalfa.There were obvious differences in using the six types of carbon sources between mulberry and alfalfa treatments.Nitrogen and intercropping increased the numbers of sole carbon substrate in mulberry treatments where the relative use rate exceeded 4%.While the numbers declined in alfalfa with nitrogen and intercropping.RDA indicated that URE was positive when intercropping mulberry was treated with nitrogen,but was negative in monoculture alfalfa treated with nitrogen.Soil pH and SWC were positive with mulberry treatments but were negative with alfalfa treatments.Intercropping with alfalfa benefited mulberry in the absence of nitrogen application.Intercropping with alfalfa and nitrogen application could improve the microbial community function and diversity in rhizosphere soil of mulberry.The microbial community in rhizosphere soil of mulberry and alfalfa is strategically complementary in terms of using carbon sources.

The role of organic and inorganic substituents of roxarsone determines its binding behavior and mechanisms onto nano-ferrihydrite colloidal particles

The retention and fate of Roxarsone(ROX)onto typical reactive soil minerals were crucial for evaluating its potential environmental risk.However,the behavior and molecular-level reaction mechanism of ROX and its substituents with iron(hydr)oxides remains unclear.Herein,the binding behavior of ROX on ferrihydrite(Fh)was investigated through batch experiments and in-situ ATR-FTIR techniques.Our results demonstrated that Fh is an effective geo-sorbent for the retention of ROX.The pseudo-second-order kinetic and the Langmuir model successfully described the sorption process.The driving force for the binding of ROX on Fh was ascribed to the chemical adsorption,and the rate-limiting step is simultaneously dominated by intraparticle and film diffusion.Isotherms results revealed that the sorption of ROX onto Fh appeared in uniformly distributed monolayer adsorption sites.The twodimensional correlation spectroscopy and XPS results implied that the nitro,hydroxyl,and arsenate moiety of ROX molecules have participated in binding ROX onto Fh,signifying that the predominated mechanisms were attributed to the hydrogen bonding and surface complexation.Our results can help to better understand the ROX-mineral interactions at the molecular level and lay the foundation for exploring the degradation,transformation,and remediation technologies of ROX and structural analog pollutants in the environment.