[Shifts in Rhizosphere Bacterial Community Structure, Co-occurrence Network, and Function of Miscanthus Following Cadmium Exposure].

As a representative of second-generation bioenergy plants, Miscanthus has received increasing attention in the studies of heavy metal (HM)-contaminated soil remediation. Currently, few studies have examined the effects of using Miscanthus to remediate HM-contaminated soils on the composition and function of microbial communities. In this study, the Miscanthus cultivar M. saccariflorus was examined for its tolerance and enrichment abilities when grown in soils containing 100 mg ·kg-1 of cadmium (Cd). The structure, function, and co-occurrence network of their rhizosphere bacterial communities were analyzed during the remediation process. MiSeq sequencing showed that the Miscanthus rhizosphere bacterial community comprised 32 phyla and 425 genera, including plant growth-promoting rhizobacteria (PGPR), such as Sphingomonas, Bacillus, Gemmatimonas, and Streptomyces. The addition of Cd affected the Miscanthus rhizosphere bacterial community and reduced community diversity. Phylogenetic molecular ecological networks indicated that Cd addition reduced the interactions between Miscanthus rhizosphere bacteria to generate a simpler network structure, increased the number of negative-correlation links, enhanced the competition between rhizosphere bacterial species, and changed the composition of key bacteria. PICRUSt functional predictive analysis indicated that Cd stress reduced soil bacterial functions in the Miscanthus rhizosphere. The results of this study provide a reference for the subsequent regulation of efficient Miscanthus remediation by PGPRs or key bacteria.

[Spatiotemporal variation of epilithic algae in Xiangxi River system].

Xiangxi River system is the greatest branch in the Hubei reservoir area of the Three Gorges reservoir. In this paper, the epilithic algae in the River and its three major tributaries were investigated from July 2005 to June 2006. A total of 218 taxa were identified, including 183 species of Bacillariophyta, 24 species of Chlorophyta, 10 species of Cyanophyta, and one species of Xanthophyta. The diatom Achnanthes linearis was the most predominant species. The richness and Shannon-Wiener diversity indices varied significantly (or almost significantly) over time and space, and the total average values were 32 and 1.54, respectively. The total averages of annual epilithic algal density and chlorophyll a concentration were 8.75 x 10(9) cells x m(-2) and 14.62 mg x m(-2), respectively. There were significant differences in the algal density and chlorophyll a concentration among different sampling sites, and the maximum values were observed in Gufu River tributary, which were one order of magnitude higher than the minimum ones in Jiuchong River tributary. The algal density and chlorophyll a concentration tended to be higher in winter and spring than in summer and autumn, but no significant differences were observed in various seasons. Epilithic algal density and chlorophyll a concentration were significantly negatively correlated with elevation and water current, but positively correlated with the total nitrogen concentration in water.

[Spatial distribution of macroinvertebrates in Xiangxi River].

An investigation was made from July 2005 to June 2006 to understand the spatial distribution of macroinvertebrates in Xiangxi River, the largest tributary in Hubei portion of Three Gorges Reservoir. The results showed that Ephemeroptera baetis spp., Ephemeroptera epeorus spp., and Plecoptera nemoura spp. were the dominant taxa. There existed greater differences in the habitat characters and in the community structure of macroinvertebrates among the major tributaries of Xiangxi River, and the relative abundance of functional feeding groups could reflect the characters of different habitats. A comparison of the diversity of dominant taxa and their tolerance towards pollution among the major tributaries showed that Jiuchong River had the best habitat, followed by the main stream of Xiangxi River, and Gaolan River and Gufu River. Canonical correspondence analysis showed that the NH4+ -N concentration in the main stream of Xiangxi River, the pH, turbidity, water depth, SiO2, conductance, and alkalinity in Jiuchong River, the turbidity in Gaolan River, and the NH4+ -N and NO3- -N concentrations in Gufu River had significant impact on the community structure of macroinvertebrates.

[Influence of cascaded exploitation of small hydropower on phytoplankton in Xiangxi River].

With the five small hydropowers (SHPs) from up- to downstream of Xiangxi River as test objects, this paper studied the influence of SHPs cascaded exploitation on the phytoplankton in the river. The results showed that phytoplankton assemblages were dominated by diatoms, occupying 95.54% of the total number of species. Achnanthes linearis, A. lanceolata var. elliptica and Cocconeis placentula were the most abundant species, with the relative abundance being 23.96%, 18.62% and 12.48%, respectively. The average algal density at 25 sampling sites was 6.29 x 10(5) ind x L(-1), with the maximum of 1.81 x 10(6) ind x L(-1) and the minimum of 2.35 x 10(5) ind x L(-1). Two-way ANOVA indicated that water flow velocity was the main factor affecting the phytoplankton. The establishment of the cascaded SHPs on the river made the habitat of lower reach has a significant difference with the others, resulting in a dramatic change of many parameters including Margalef diversity index, species richness, generic richness, taxonomic composition, and the percentage of diatoms.