Dam construction significantly influences riparian ecological functions and environmental conditions in the reservoir region. Despite the importance of diazotrophic mediation of nitrogen cycling in riparian ecosystems, knowledge concerning the impacts of dam construction on diazotrophic function and community composition remains very limited. Here, riparian soils were collected from control sites and dam-affected sites located in six cascade dam-formed reservoirs on the Lancang River, China. Diazotrophic activity was assessed by measuring nitrogen fixation rate, while bacterial abundance and community composition were determined with the nifH gene, using quantitative real-time polymerase chain reaction and MiSeq sequencing, respectively. The results indicate that the activity, abundance, and ɑ-diversity of diazotrophs in the affected sites were significantly higher than those in the control sites. The diazotrophic community composition was differed between the control and affected sites, with the latter showing significantly lower community dissimilarity than the control. Both geographic distance and environmental heterogeneity varied in the diazotrophic community, while environmental heterogeneity was the primary factor controlling diazotrophic assemblage in riparian soils, especially at the affected sites. Moreover, co-occurrence network analyses revealed a much higher possible network connectivity at the affected sites than at the control sites. This study suggests distinct activity, abundance, distribution pattern, and network structure of the diazotrophic populations in riparian soils between dam-affected and control sites; thus, providing a novel insight into the potential ecological effects of dam construction on nitrogen cycling.

Dam construction alters function and community composition of diazotrophs in riparian soils across an environmental gradient

. Bacteria are widely distributed in atmospheric aerosols and are indispensable components of clouds, playing an important role in the atmospheric hydrological cycle. However, limited information is available about the bacterial community structure and function, especially for the increasing air pollution in the North China Plain. Here, we present a comprehensive characterization of bacterial community composition, function, variation, and environmental influence for cloud water collected at Mt Tai from 24 July to 23 August 2014. Using Miseq 16S rRNA gene sequencing, the highly diverse bacterial community in cloud water and the predominant phyla of Proteobacteria, Bacteroidetes, Cyanobacteria, and Firmicutes were investigated. Bacteria that survive at low temperature, radiation, and poor nutrient conditions were found in cloud water, suggesting adaption to an extreme environment. The bacterial gene functions predicted from the 16S rRNA gene using the Phylogenetic Investigation of Communities by Reconstruction of Unobserved States (PICRUSt) suggested that the pathways related to metabolism and disease infections were significantly correlated with the predominant genera. The abundant genera Acinetobacter, Stenotrophomonas, Pseudomonas, and Empedobacter originated from a wide range of habitats including cloud condensation nuclei and ice nuclei active species, opportunistic pathogens, and functional species, demonstrating the importance of ecology and health in cloud water. Cluster analysis including hierarchical cluster (Hcluster) and principal coordinate analysis (PCoA) indicated a significant disparity between polluted and non-polluted samples. Linear discriminant analysis effect size (LEfSe) demonstrated that potential pathogens were enriched in the polluted cloud samples, whereas the diverse ecological function groups were significant in the non-polluted samples. Discrepant community structure determined by redundancy analysis (RDA) indicated that the major ions in cloud water and PM2. 5 in the atmosphere have a negative impact on bacteria, playing a vital role in shaping microbial community structure. The major ions might provide nutrition to bacteria and directly influence the bacterial community, whereas PM2. 5 in air has an indirect impact on bacterial community structure. During wet deposition, soluble particulate matter was dissolved in water droplets resulting in elevated concentration in cloud water. PM2. 5 was possibly associated with different origins and pathways of air mass as determined using source tracking by the backward trajectory, mainly related to long-range transport. This work enhanced our understanding of the characteristics of bacterial ecology in the atmospheric aqueous phase, highlighting the potential influence of environmental variables on the bacterial community in cloud processes. It may provide fundamental information of the bacterial community response in cloud water under increasing pollution. However, due to the limited sample size (13 samples) collected at the summit of Mt Tai, these issues need in-depth discussion. Further studies based on an annual series of field observation experiments and laboratory simulations will continue to track these issues.

/pdf/characteristics-of-bacterial-community-in-cloud-water-at-mt-4io9l134a3.pdf

Characteristics of bacterial community in cloud water at Mt Tai: similarity and disparity under polluted and non-polluted cloud episodes

The use of leaf mulch as a soil cover is effective in improving yield and soil fertility. The field experiment was conducted during 2010 and 2011 to study the effect of plant spacing (30 cm × 30 cm and 45 cm × 30 cm) and four mulches {pine needles (Pinus roxburghii), poplar leaf (Populus deltoides), silver oak (Grevillea robusta) tree leaf mulch and unmulched control} on growth, yield, quality of stevia and soil fertility. Weed count and dry weed weight was not affected by spacing levels during August and at the time of harvest, whereas, in unmulched plots it was significantly higher than mulched plots. Dry leaf yield, total dry biomass and leaf area index (LAI) were significantly higher in 30 cm × 30 cm spacing level and poplar leaf mulch. All the mulched plots significantly increased organic carbon (OC), available nitrogen (N), phosphorus (P) and potassium (K), bacterial and fungal population compared to unmulched plots. Rebaudioside-A content was higher in plots mulched with poplar leaves. Steviol glycosides were not significantly affected by different treatments. Soil biological activities were also enhanced by tree leaf mulches. Leaf mulch enhanced microbial biomass, relative to non-mulched soils, likely via improving C and water availability for soil microbes.

http://ijpp.gau.ac.ir/article_1612_9e392e620cb2122ca12bde975af19bd2.pdf

Effect of plant spacing and organic mulch on growth, yield and quality of natural sweetener plant Stevia and soil fertility in western Himalayas

In order to evaluate the genetic diversity of cyanophage communities of rice fields, viral capsid assembly protein gene (g20) was amplified with primers CPS1 and CPS8. The DNA was extracted three times from viral concentrates obtained from floodwater samples collected in each of four different plots (no fertilizer; P and K chemical fertilizers; N, P, and K chemical fertilizers; and chemical fertilizers with compost). Denaturing gradient gel electrophoresis (DGGE) gave different g20 clones. The sequencing of DGGE bands revealed that the g20 genes of the floodwater were divergent and that the majority of clones formed several unique groups. However, they were more closely related to g20 sequences from freshwaters than to those from marine waters, suggesting that g20 genes in terrestrial aquatic environments are different from those in marine environments.

Unique viral capsid assembly protein gene (g20) of cyanophages in the floodwater of a Japanese paddy field

To estimate diversity, seasonal variation, and phylogeny of the cyanobacterial communities in rice straw placed in nylon mesh bags and left on the soil surface of a paddy field, total DNA was extracted from straw, amplified by polymerase chain reaction targeting 16S rRNA genes of cyanobacteria, and the amplicons were separated by denaturing gradient gel electrophoresis (DGGE). These DGGE bands were sequenced. The paddy field was under flooded condition after transplanting of rice (Experiment 1) and under drained conditions after harvest (Experiment 2). The residual samples on the soil surface under upland conditions were collected just before spring plowing and were placed again on the soil surface after transplanting under flooded conditions. DGGE band patterns of cyanobacterial communities of rice straw were different under drained conditions, under flooded conditions when fresh rice straw samples were placed (Experiment 1), and under flooded conditions when residual rice straw samples were replaced (Experiment 2), indicating that the communities were influenced by both water regime of the paddy field and the degree of the rice straw decomposition. Sequence analysis of DGGE bands indicated that most of the cyanobacteria in rice straw on the soil surface in the paddy field were filamentous members belonging to Subsections III and IV. Filamentous cyanobacterial cells were observed in rice straw under flooded conditions by epifluorescence microscopy.

https://link.springer.com/content/pdf/10.1007%2Fs00374-007-0244-4.pdf

Cyanobacterial communities of rice straw left on the soil surface of a paddy field

Organic substances viz., sewage and slurry, compost, farmyard manure (FYM) and green manure used in the study under different moisture regimes had a varied effect on cyanobacterial nitrogenase activity and its distributional pattern. Green manure source was the most effective in enhancing cyanobacterial nitrogenase activity, followed by FYM, compost and sewage and slurry. A better response was observed in soils under waterlogged than under moist conditions. A gradual increase in nitrogenase activity was recorded up to one per cent organic carbon both in vitro and in vivo. The cyanobacterial diversity was maximum in sewage and slurry sites.

Influence of source of organics and soil organic matter content on cyanobacterial nitrogen fixation and distributional pattern under different water regimes

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Influence of source of organics and soil organic matter content on cyanobacterial nitrogen fixation and distributional pattern under different water regimes