Search

It's vital to explore critical indicators when identifying potential pollution sources of urban rivers. However, the variations of urban river water qualities following temporal and spatial disturbances were highly local-dependent, further complicating the understanding of pollution emission laws. In order to understand the successional trajectory of water qualities of urban rivers and the underlying mechanisms controlling these dynamics at local scale, we collected daily monitoring data for 17 physical and chemical parameters from seven on-line monitoring stations in Nanfeihe River, Anhui, China, during the year 2018. The water quality at tributaries were similar, while that at main river was much different. A seasonal ''turning-back" pattern was observed in the water quality, which changed significantly from spring to summer but finally changed back in winter. This result was possibly regulated by seasonally-changed dissolved oxygen and water temperature. Linear mixed models showed that the site 2, with the highest loads of pollution, contributed the highest (β = 0.316, P < 0.001) to the main river City Water Quality Index (CWQI) index, but site 5, the geographically nearest site to main river monitoring station, did not show significant effect. In contrast, site 5 but not site 2 contributed the highest (β = 0.379, P < 0.001) to the main river water quality. Therefore, CWQI index was a better index than water quality to identify potential pollution sources with heavy loads of pollutants, despite temporal and spatial disturbances at local scales. These results highlight the role of aeration in water quality controlling of urban rivers, and emphasized the necessity to select proper index to accurately trace the latent pollution sources. [ABSTRACT FROM AUTHOR]

Fire is a crucial event regulating the structure and functioning of many ecosystems. Yet few studies have focused on how fire affects taxonomic and functional diversities of soil microbial communities, along with changes in plant communities and soil carbon (C) and nitrogen (N) dynamics. Here, we analyze these effects in a grassland ecosystem 9 months after an experimental fire at the Jasper Ridge Global Change Experiment site in California, USA. Fire altered soil microbial communities considerably, with community assembly process analysis showing that environmental selection pressure was higher in burned sites. However, a small subset of highly connected taxa was able to withstand the disturbance. In addition, fire decreased the relative abundances of most functional genes associated with C degradation and N cycling, implicating a slowdown of microbial processes linked to soil C and N dynamics. In contrast, fire stimulated above‐ and belowground plant growth, likely enhancing plant–microbe competition for soil inorganic N, which was reduced by a factor of about 2. To synthesize those findings, we performed structural equation modeling, which showed that plants but not microbial communities were responsible for significantly higher soil respiration rates in burned sites. Together, our results demonstrate that fire ‘reboots’ the grassland ecosystem by differentially regulating plant and soil microbial communities, leading to significant changes in soil C and N dynamics.Fire significantly increased environmental selection pressure on soil microbial community, where a small subset of highly connected taxa was able to withstand the disturbance. Fire decreased the relative abundances of most functional genes associated with C degradation and N cycling, but stimulated above‐ and belowground plant growth, likely enhancing plant–microbe competition for soil inorganic N. Plants but not microbial communities were responsible for significantly higher soil respiration rates in burned sites. [ABSTRACT FROM AUTHOR]

Abstract The continuously increasing concentration of atmospheric CO 2 has considerably altered ecosystem functioning. However, few studies have examined the long-term (i.e. over a decade) effect of elevated CO 2 on soil microbial communities. Using 16S rRNA gene amplicons and a GeoChip microarray, we investigated soil microbial communities from a Californian annual grassland after 14 years of experimentally elevated CO 2 (275 ppm higher than ambient). Both taxonomic and functional gene compositions of the soil microbial community were modified by elevated CO 2. There was decrease in relative abundance for taxa with higher ribosomal RNA operon (rrn) copy number under elevated CO 2 , which is a functional trait that responds positively to resource availability in culture. In contrast, taxa with lower rrn copy number were increased by elevated CO 2. As a consequence, the abundance-weighted average rrn copy number of significantly changed OTUs declined from 2.27 at ambient CO 2 to 2.01 at elevated CO 2. The nitrogen (N) fixation gene nifH and the ammonium-oxidizing gene amoA significantly decreased under elevated CO 2 by 12.6% and 6.1%, respectively. Concomitantly, nitrifying enzyme activity decreased by 48.3% under elevated CO 2 , albeit this change was not significant. There was also a substantial but insignificant decrease in available soil N, with both nitrate (NO 3 −) (−27.4%) and ammonium (NH 4 +) (−15.4%) declining. Further, a large number of microbial genes related to carbon (C) degradation were also affected by elevated CO 2 , whereas those related to C fixation remained largely unchanged. The overall changes in microbial communities and soil N pools induced by long-term elevated CO 2 suggest constrained microbial N decomposition, thereby slowing the potential maximum growth rate of the microbial community. Graphical abstract Unlabelled Image Highlights • Effects of 14 years of experimentally elevated CO 2 on soil microbes in a semi-arid grassland were examined. • The abundance-weighted average rrn copy number of significantly changed OTUs declined by elevated CO 2. • The nitrogen fixation gene nifH and the ammonium-oxidizing gene amoA significantly decreased by elevated CO 2. • Elevated CO 2 constrained microbial N decomposition, thereby slowing potential maximum growth rate of microbial community. [ABSTRACT FROM AUTHOR]

Biomass-derived carbon-based materials represent a promising class of candidates for supercapacitors. Herein, we developed a new route for the fabrication of biomimetic layered microporous carbon for high-performance supercapacitors by hybridizing konjac glucomannan (KGM) with cysteine (Cys) using a cost-efficient method. When the mass ratio of Cys/KGM was 1 : 6 and the carbonized temperature was 800 °C (denoted as Cys/KGM-800-6), Cys/KGM-800-6 retained the atomic ratio of 5.89% nitrogen atoms. Additionally, the proportion of micropores in Cys/KGM-800-6 reached 93.02% with an average micropore diameter of 2.16 nm. In the capacitance test, the specific capacitance of Cys/KGM-800-6 was 351.7 F g−1 and 226 F g−1 at the current densities of 1 A g−1 and 20 A g−1, respectively. After 10 000 charge–discharge cycles, the hybrid materials maintained 95.57% of the specific capacitance of the pristine material at the current density of 1 A g−1. This work demonstrates a potential synthetic method for boosting the performance of carbon-based supercapacitors through the hybridization of common natural biomass and amino acid. [ABSTRACT FROM AUTHOR]

It is of great interest to elucidate underlying mechanisms to maintain stability of anaerobic digestion, an important process in waste treatment. By operating triplicate anaerobic digesters continuously for two years, we found that microbial community composition shifted over time despite stable process performance. Using an association network analysis to evaluate microbial interactions, we detected a clear successional pattern, which exhibited increasing modularity but decreasing connectivity among microbial populations. Phylogenetic diversity was the most important factor associated with network topology, showing positive correlations with modularity but negative correlations with network complexity, suggesting induced niche differentiation over time. Positive, but not negative, correlation strength was significantly related ( p < 0.05) to phylogeny. Furthermore, among populations exhibiting consistent positive correlations across networks, close phylogenetic linkages were evident (e.g. Clostridiales organisms). Clostridiales organisms were also identified as keystone populations in the networks (i.e., they had large effects on other species), suggestive of an important role in maintaining process stability. We conclude that microbial interaction dynamics of anaerobic digesters evolves over time during stable process performance. [ABSTRACT FROM AUTHOR]