Analysis of the influence paths of land use and landscape pattern on organic matter decomposition in river ecosystems: Focusing on microbial groups

Linking pharmaceutical residues to dissolved organic matter and aquatic bacterial communities in a highly urbanized bay

Pharmaceuticals are causing environmental concerns associated with their widespread distribution in aquatic ecosystems. The environmental fate and behavior of pharmaceutical residues are related to dissolved organic matter and bacterial communities, both of which are strongly influenced by human activities. However, the relationships among pharmaceutical pollution, dissolved organic matter pool, and bacterial community structure under the pressure of human activities are still unclear, especially in highly urbanized bay areas. In this study, we investigated the occurrence and distribution of 35 pharmaceuticals in a typical urbanized bay (Hangzhou Bay) in Eastern China, and analyzed their relationships with dissolved organic matter and aquatic bacterial community structure. The target pharmaceuticals were ubiquitously detected in surface water samples, with their concentrations ranging from undetectable to 263 ng/L. The detected pharmaceuticals were mostly sulfonamides, macrolides, antidepressants, and metabolites of stimulants. Significant positive correlations were observed between the concentrations of pharmaceuticals and the intensity of human activities. Strong correlations also emerged between the concentration of antidepressants and the speed of urban expansion, as well as between the concentration of cardiovascular drugs and the population density or nightlight index. Three fluorescent components (protein-like C1, terrestrial humic-like C2, protein tryptophan-like C3) were significantly positively correlated with the total concentration of pharmaceuticals. Pharmaceutical pollution reshaped aquatic bacterial communities, based on the close correlation observed between pharmaceutical concentration and bacterial community structure. The results elucidate the potential dynamics of dissolved organic matter pool and aquatic bacterial communities in response to pharmaceutical pollution in urbanized bay ecosystems.

Involvement of exogenous arsenic-reducing bacteria in root surface biofilm formation promoted phytoextraction of arsenic

Root surface biofilm (RSB) is the last window for pollutants entering plant roots and thus plays a critical role in the phytoextraction of pollutants. Exogenous arsenic-reducing bacteria (EARB) have been adopted to enhance the phytoextraction of arsenic (As). However, whether EARB would be involved in RSB formation together with indigenous bacteria and the role of EARB involvement in As phytoextraction are still unknown. Herein, two EARB strains and two phytoextractors (wheat and maize) were selected to investigate the involvement of EARB in RSB formation and its role in As phytoextraction. Results showed that EARB successfully participated in RSB formation together with indigenous bacteria, attributing to their strong chemotaxis and biofilm formation abilities induced by root exudates. The involvement of EARB in RSB formation significantly enhanced As accumulation in plant roots, since more arsenite (As(III)) caused by arsenate (As(V)) reduction in RSB was absorbed by roots. Its underlying mechanism was further elucidated. EARB involvement increased phylum Proteobacteria to produce more siderophores in RSB. Siderophores then improved photosynthesis by increasing catalase and peroxidase activities and decreasing the malondialdehyde of plants. These actions further raised the shoot fresh weight to enhance As accumulation in plant roots. Moreover, mesophyll cell in wheat has a stronger As(V) reduction ability than that in maize, resulting in opposite distribution patterns of As(III) and As(V) in wheat and maize shoots. This study provides a new understanding of phytoextraction enhanced by exogenous bacteria and fills the gap in the role of EARB in As phytoextraction from the perspective of the RSB microregion.

Evaluation of ethylicin as a potential soil fumigant in commercial tomato production in China

Recent increases in soil-borne plant disease have limited further expansion of some crops produced in protected agriculture. Soil fumigation effectively minimizes the impact of soil pathogens causing many diseases. We provide the first report of the efficacy of the Chinese fungicide ethylicin as a soil fumigant against the plant pathogens such as Fusarium spp. and Phytophthora spp., and against the plant parasitic nematode Meloidogyne spp. We also examined ethylicin's impact on the physicochemical properties of soil, the soil's bacterial and fungal taxonomic composition, the plant growth of tomatoes, the enzyme activity of soil and tomato yield. Ethylicin fumigation significantly decreased the abundance of Fusarium spp. and Phytophthora spp. by 67.7 %-84.0 % and 53.8 %-81.0 %, respectively. It reduced Meloidogyne spp. by 67.2 %-83.6 %. Ethylicin significantly increased the growth of tomato plants and tomato yield by 18.3 %-42.0 %. The soil's ammonium‑nitrogen concentration increased significantly in answer to ethylicin fumigation, while nitrate‑nitrogen concentration and the activity of soil urease decreased significantly. High-throughput gene sequencing had been used to show that ethylicin cut down the taxonomic soil bacteria diversity and bacterial abundance, but increased the soil fungi taxonomic diversity. Some genera of microorganisms increased, such as Firmicutes, Steroidobacter and Chytridiomycota, possibly due to changes in the physicochemical properties of soil that differentially favored their survival. We conclude that ethylicin is efficacious as a soil fumigant and it would be a useful addition to the limited number of soil fumigants currently available.

Insights from the Niger Delta Region, Nigeria on the impacts of urban pollution on the functional organisation of Afrotropical macroinvertebrates

Anthropogenic activities, including urbanisation and industrialisation threaten stream ecological integrity, ecosystem community structure and ecosystem functioning of rivers and streams worldwide. However, developing sustainable monitoring strategies for ecological health remains a critical challenge in Africa. We examined the effects of urban disturbance on macroinvertebrate Functional Feeding Groups in selected streams in the Niger Delta Region of Nigeria. We sampled 11 sites between 2008 and 2012 and grouped into three site groups (Site groups 1 > 2 > 3). The groups represent an increasing gradient of urban pollution. Our result showed that urban-induced disturbances affected physicochemical variables in the study area (PERMANOVA; p < 0.05), with nutrients NO₂-N, PO₄-P, and electrical conductivity being significantly higher in impacted Site group 3 (ANOVA, p < 0.05). Predators and gatherers were the most dominant Functional Feeding Group recorded in the study area, while shredders were the least abundant macroinvertebrate Functional Feeding Groups. The multivariate RLQ analysis revealed that shredders, predators, and scrapers were tolerant of urban pollution, whereas gatherers were sensitive to increasing urban pollution. Overall, macroinvertebrates Functional Feeding Groups responded differentially to urban pollution in the Niger Delta Region. Identifying pollution indicator Functional Feeding Groups is seen as an important step towards developing a reliable, low-cost tool for riverine monitoring of urban pollution effects in Africa.