The characteristics of natural organic matter (NOM) released from a representative forest soil under acidic, neutral and basic conditions were investigated based on their physicochemical properties and activated carbon adsorbability. For physicochemical properties, it was found that as the releasing condition changed from acidic to basic, NOM components possessing larger UV absorbing capability and larger molecular weight were released into water. The DOC concentration of NOM released under basic condition was tens of times larger than that under either acidic or neutral condition. On the other hand, based on the batch adsorption experiments and isotherm data analysis with a modified Freundlich isotherm model, the differences in the adsorbability of the released NOM were also demonstrated. Compared to the NOM released under either neutral or basic condition, the NOM released under acidic condition was less adsorbable, and NOM components with larger molecular weight seemed to be more preferentially adsorbed.
Mangrove trees generally play important roles in protecting intertidal ecosystems. The mangrove root-associated sediments provide a repertoire of microbial communities that contribute to pivotal ecological functions in the system. In the present study, we used the high-throughput sequencing and PICRUSt-predicted functional information (based on 16S/18S rDNA profiles) to investigate the bacterial, archaeal, and fungal communities in two mangrove systems, located in the estuary of the Jiulong River (China), with different contaminated conditions and frequencies of human activity. Diverse distribution patterns for microbial communities were observed in six sediment samples collected from the two survey areas, which were found to be related mainly to the substrates in mangrove sediments. The sediments were predominated by relatively higher ratios of heterotrophic bacteria that participated in the degradation of organic matters, including phylum of Chloroflexi, Acidobacteriota, Desulfobacterota, and Proteobacteria. In addition, Crenarchaeota and Ascomycota presented the highest abundances of archaea and fungi, respectively. The relatively high concentrations of calcium, nitrogen, magnesium, and phosphorus in mangrove sediments correlated significantly with the microbial communities. In addition, although the potential functions were similar in the two sites based on COG and KEGG pathways, the abundances of enzymes involved in the degradation processes of cellulose and hemicellulose and the metabolism of nitrogen and sulfur presented distinctions. These results provide insights into the environmental conditions shaping microbial assemblies of the mangrove sediments under the impacts of human activities; for instance, a more abundant amount of calcium was found in urban areas in this study.
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