Phytoplankton Communities Exhibit a Stronger Response to Environmental Changes than Bacterioplankton in Three Subtropical Reservoirs.

The simultaneous analysis of multiple components of ecosystems is crucial for comprehensive studies of environmental changes in aquatic ecosystems, but such studies are rare. In this study, we analyzed simultaneously the bacterioplankton and phytoplankton communities in three Chinese subtropical reservoirs and compared the response of these two components to seasonal environmental changes. Time-lag analysis indicated that the temporal community dynamics of both bacterioplankton and phytoplankton showed significant directional changes, and variance partitioning suggested that the major reason was the gradual improvement of reservoir water quality from middle eutrophic to oligo-mesotrophic levels during the course of our study. In addition, we found a higher level of temporal stability or stochasticity in the bacterioplankton community than in the phytoplankton community. Potential explanations are that traits associated with bacteria, such as high abundance, widespread dispersal, potential for rapid growth rates, and rapid evolutionary adaptation, may underlie the different stability or stochasticity of bacterioplankton and phytoplankton communities to the environmental changes. In addition, the indirect response of bacterioplankton to nitrogen and phosphorus may result in the fact that environmental deterministic selection was stronger for the phytoplankton than for the bacterioplankton communities

The biogeography of abundant and rare bacterioplankton in the lakes and reservoirs of China.

Bacteria play key roles in the ecology of both aquatic and terrestrial ecosystems; however, little is known about their diversity and biogeography, especially in the rare microbial biosphere of inland freshwater ecosystems. Here we investigated aspects of the community ecology and geographical distribution of abundant and rare bacterioplankton using high-throughput sequencing and examined the relative influence of local environmental variables and regional (spatial) factors on their geographical distribution patterns in 42 lakes and reservoirs across China. Our results showed that the geographical patterns of abundant and rare bacterial subcommunities were generally similar, and both of them showed a significant distance-decay relationship. This suggests that the rare bacterial biosphere is not a random assembly, as some authors have assumed, and that its distribution is most likely subject to the same ecological processes that control abundant taxa. However, we identified some differences between the abundant and rare groups as both groups of bacteria showed a significant positive relationship between sites occupancy and abundance, but the abundant bacteria exhibited a weaker distance-decay relationship than the rare bacteria. Our results implied that rare subcommunities were mostly governed by local environmental variables, whereas the abundant subcommunities were mainly affected by regional factors. In addition, both local and regional variables that were significantly related to the spatial variation of abundant bacterial community composition were different to those of rare ones, suggesting that abundant and rare bacteria may have discrepant ecological niches and may play different roles in natural ecosystems

Denitrifier community in the oxygen minimum zone of a subtropical deep reservoir.

Denitrification is an important pathway for nitrogen removal from aquatic systems and this could benefit water quality. However, little is known about the denitrifier community composition and key steps of denitrification in the freshwater environments, and whether different bacteria have a role in multiple processes of denitrification reduction. In this study, quantitative PCR, quantitative RT-PCR, clone library and 454 pyrosequencing were used together to investigate the bacterial and denitrifier community in a subtropical deep reservoir during the strongly stratified period. Our results indicated that the narG gene recorded the highest abundance among the denitrifying genes (2.76×109 copies L-1 for DNA and 4.19×108 copies L-1 for RNA), and the lowest value was nosZ gene (7.56×105 copies L-1 for DNA and undetected for RNA). The RNA: DNA ratios indicated that narG gene was the most active denitrifying gene in the oxygen minimum zone of Dongzhen Reservoir. Further, α-, β- and γ- Proteobacteria were the overwhelmingly dominant classes of denitrifier communities. Each functional gene had its own dominant groups which were different at the genus level: the narG gene was dominated by Albidiferax, while nirS gene was dominated by Dechloromonas. The main OTU of nirK gene was Rhodopseudomonas palustris, but for norB and nosZ genes, they were Bacillus and Bradyrhizobium, respectively. These results contribute to the understanding of linkages between denitrifier community, function and how they work together to complete the denitrification process. Studies on denitrifier community and activity may be useful in managing stratified reservoirs for the ecosystem services and aiding in constructing nitrogen budgets

Relative abundance of different denitrifying genes at the genus (or species) level in Dongzhen Reservoir.

<p>Shown are OTUs assigned to the highest taxonomic level possible using a BLASTN in GenBank database. The circle size corresponds to the relative average abundance OTUs for each denitrifying gene.</p

Scheme for nitrogen transformation from NO₃⁻ to N₂ by denitrification.

<p>Genes encoding enzymes that mediate the denitrification steps include those for nitrate reductase (<i>narG</i>), nitrite reductase (<i>nirS</i>/<i>nirK</i>), nitric oxide reductase (<i>norB</i>) and nitrous oxide reductase (<i>nosZ</i>).</p

Bacterial community compositions at phylum level and Proteobacteria at class level revealed by clone library and 454 pyrosequencing.

<p>Bacterial community compositions at phylum level and Proteobacteria at class level revealed by clone library and 454 pyrosequencing.</p

Evidence for two different morphotypes of Difflugia tuberspinifera from China

National Basic Research Program of China [2012CB956103]; National Natural Science Foundation of China [31370471, 31172114, 30800097]; Natural Science Foundation for Distinguished Young Scholars of Fujian Province [2012706009]Difflugia is a morphologically diverse genus of testate amoebae, which are common components of freshwater ecosystems. We observed a new morphotype similar to Diffiugia tuberspinifera but without spine in four Xiamen reservoirs, Fujian Province, southeast China. We investigated its morphology and biometry using light and scanning electron microscopy. The linear discriminant analysis and principal component analysis of biometric characters revealed that the spiny and spineless forms of D. tuberspinifera differed only in the presence or absence of spine. Shell height, shell diameter, aperture diameter and collar height did not differ significantly between the two morphotypes. The number of conical spines varies from 0 to 8. However, the distribution of spine numbers showed two main modes at 0 (spineless form 45.1% of individuals) and 4-6 (38.9%), suggesting the possible existence of two genetically distinct lineages. Spines may have ecological and evolutionary significance. Our results suggested that the spiny and spineless morphotypes of D. tuberspinifera represent either a single variable taxon with different ecotypes or sibling species. Further morphological studies on clonal variations and molecular approaches are needed to clarify if the spineless morph represents an independent species or not. (C) 2013 Elsevier GmbH. All rights reserved

Relative abundance of different bacterial groups from 16 S rRNA gene and five denitrifying genes based on the clone library analysis.

<p>Relative abundance of different bacterial groups from 16 S rRNA gene and five denitrifying genes based on the clone library analysis.</p

Environmental variables in the oxygen minimum zone of Dongzhen Reservoir in October 2011.

<p>Values are mean ± SE (n = 3).</p

Map of Xiamen offshore sea area showing the locations of twelve sampling sites.

<p>Map of Xiamen offshore sea area showing the locations of twelve sampling sites.</p