ABSTRACT
Release of nanoceria (nCeO2) into the environment has caused much concern about its potential toxicity, which still remains poorly understood for soil microorganisms. In this study, nanoceria and cerium (III) nitrate at different doses (10, 100 and 500 mg/kg) were applied to bok choy (Brassica rapa subsp. chinensis), grown in potting soil, to investigate the responses of soil bacterial communities to nanoceria (NC) and ionic cerium (IC) applications. The results showed that bacterial richness was slightly increased in all cerium treatments relative to the negative control without cerium amendment (CK), but a significant increase was only found in IC500. The patterns of bacterial community composition, predicted functions and phenotypes of all NC treatments were significantly differentiated from IC and CK treatments, which was correlated with the contents of cerium, available potassium and phosphorus in soil. The co-occurrence network of bacterial taxa was more complex after exposure to ionic cerium than to nanoceria. The keystone taxa of the two networks were entirely different. Predicted functions analysis found that anaerobic and Gram-negative bacteria were enriched under nanoceria exposure. Our study implies that Proteobacteria and nitrifying bacteria were significantly enriched after exposure to nanoceria and could be potential biomarkers of soil environmental perturbation from nanoceria exposure.
ABSTRACT
A located field experiment of applying phosphorus bacteria fertilizer for five years was carried out to study the effects of applying phosphorus bacteria fertilizer on the characteristics of microbial community structure in reclaimed soil. We studied the diversity of bacterial community using 16S rDNA gene sequencing and analyzed the relationship between bacterial community and Olsen-P, alkaline phosphatase. Seven treatments including control, chemical fertilizer, manure, manure and chemical fertilizer, chemical fertilizer and phosphorus bacteria, manure and phosphorus bacteria, and, manure,chemical fertilizer and phosphorus bacteria were conducted. The results showed that the relative abundance of Actinobacteria and Proteobacteria in reclaimed soil was the largest, which was 21.6ï¼ -32.2ï¼ and 13.8ï¼ -28.9ï¼ , respectively. Operational taxonomic units (OTU) number and Chao1 index of the treatment of manure, chemical fertilizer and phosphorus bacteria fertilizer was 809 and 26190, which was the highest. Phosphorus bacteria fertilizer could improve the relative abundance of soil Actinomycetes and Proteobacteria and decrease that of soil Acidobacteria, Thermotogae and Nitrospira, and had stimulatory effect on Nocardioides and Flexibacter. The treatment of manure, chemical fertilizer and phosphorus bacteria fertilizer could improve the Olsen-P and alkaline phosphatase activities in reclaimed soil. Correlation coefficients between Proteobacteria and Olsen-P, alkaline phosphatase were the highest (0.900 and 0.955). To a certain extent, Proteobacteria could be used as the sensitivity index of soil phosphorus availability.
