Diagnostic strategy for the combined effects of microplastics and potentially toxic elements on microbial communities in catchment scale

Trace metals coupled with plasticisers in microplastics strengthen the denitrification function of the soil microbiome in the Qinghai Tibetan Plateau

Due to the lack of research on the co-effects of microplastics and trace metals in the environment on nitrogen cycling-related functional microorganisms, the occurrence of microplastics and one of their plasticisers, phthalate esters, as well as trace metals, were determined in soils and river sediments in the Qinghai-Tibet Plateau. Relationship between microplastics and phthalate esters in the area was determined; the co-effects of these potentially toxic materials, and key factors and pathways affecting nitrogen functions were further explored. Significant correlations between fibre- and film-shaped microplastics and phthalate esters were detected in the soils from the plateau. Copper, lead, cadmium and di-n-octyl phthalate detected significantly affected nitrogen cycling-related functional microorganisms. The co-existence of di-n-octyl phthalate and copper in soils synergistically stimulated the expression of denitrification microorganisms nirS gene and "nitrate_reduction". Additionally, di-n-octyl phthalate and dimethyl phthalate more significantly affected the variation of nitrogen cycling-related functional genes than the number of microplastics. In a dimethyl phthalate- and cadmium-polluted area, nitrogen cycling-related functional genes, especially nirK gene, were more sensitive and stressed. Overall, phthalate esters originated from microplastics play a key role in nitrogen cycling-related functions than microplastics themselves, moreover, the synergy between di-n-octyl phthalate and copper strengthen the expression of denitrification functions.

Microplastics pollution in the Asian water tower: Source, environmental distribution and proposed mitigation strategy

Microplastics generated from fragmentation of leftover plastics and industrial waste has reached in the remotely located Asian water tower (AWT) region, the 3rd pole of earth and origin site of several freshwater rivers. The accumulation of microplastics in AWT ecosystem has potential to alter the climatic condition contributing in global warming and disturbing the biodiversity structural dynamics. The present paper provides a comprehensive critical discussion over quantitative assessment of microplastics in different ecosystems (i.e. river, lakes, sediment and snow or glacier) of AWT. The hydrodynamic fate and transport of microplastics and their ecological impact on hydromorphology and biodiversity of AWT has been exemplified. Furthermore, key challenges, perspectives and research directions are identified to mitigate microplastics associated problems. During survey, the coloured polyethylene and polyurethane fibers are the predominant microplastics found in most areas of AWT. These bio-accumulated MPs alter the rhizospheric community structure and deteriorate nitrogen fixation process in plants. Significance in climate change, MPs pollution is enhancing the emissions of greenhouse gases (NH3 by ∼34% and CH4 by ∼9%), contributing in global warming. Considering the seriousness of MPs pollution, this review study can enlighten the pathways to investigate the effect of MPs and to develop monitoring tools and sustainable remediation technologies with feasible regulatory strategies maintaining the natural significance of AWT region.

Potential synergy of microplastics and nitrogen enrichment on plant holobionts in wetland ecosystems

Wetland ecosystems are global hotspots for environmental contaminants, including microplastics (MPs) and nutrients such as nitrogen (N) and phosphorus (P). While MP and nutrient effects on host plants and their associated microbial communities at the individual level have been studied, their synergistic effects on a plant holobiont (i.e., a plant host plus its microbiota, such as bacteria and fungi) in wetland ecosystems are nearly unknown. As an ecological entity, plant holobionts play pivotal roles in biological nitrogen fixation, promote plant resilience and defense chemistry against pathogens, and enhance biogeochemical processes. We summarize evidence based on recent literature to elaborate on the potential synergy of MPs and nutrient enrichment on plant holobionts in wetland ecosystems. We provide a conceptual framework to explain the interplay of MPs, nutrients, and plant holobionts and discuss major pathways of MPs and nutrients into the wetland milieu. Moreover, we highlight the ecological consequences of loss of plant holobionts in wetland ecosystems and conclude with recommendations for pending questions that warrant urgent research. We found that nutrient enrichment promotes the recruitment of MPs-degraded microorganisms and accelerates microbially mediated degradation of MPs, modifying their distribution and toxicity impacts on plant holobionts in wetland ecosystems. Moreover, a loss of wetland plant holobionts via long-term MP-nutrient interactions may likely exacerbate the disruption of wetland ecosystems' capacity to offer nature-based solutions for climate change mitigation through soil organic C sequestration. In conclusion, MP and nutrient enrichment interactions represent a severe ecological risk that can disorganize plant holobionts and their taxonomic roles, leading to dysbiosis (i.e., the disintegration of a stable plant microbiome) and diminishing wetland ecosystems' integrity and multifunctionality.

Disturbance mitigation of thiencarbazone-methyl·isoxaflutole on bacterial communities through nitrification inhibitor and attapulgite

There is a knowledge gap in the interaction between the effects of herbicide thiencarbazone-methyl·isoxaflutole on soil microflora and environmental parameters, which leads to a lack of measures in mitigating damage to bacterial communities from the herbicide use. The impacts of thiencarbazone-methyl·isoxaflutole and soil parameters on the diversity, structure and functions of soil bacterial communities were clarified, and the effects and potential mitigation mechanisms of nitrapyrin and modified attapulgite with bacterial function intervention on bacterial communities were explored through incubation and field experiments. The results showed that as thiencarbazone-methyl·isoxaflutole application increased, the stress on soil bacterial community structure and diversity also increased. The relative abundance of bacteria including Aridibacter and GP7 and functional annotations including "nitrate_reduction" were significantly negatively correlated with thiencarbazone-methyl·isoxaflutole residues in soils. The remarkable toxic effects on the Adhaeribacter bacteria were detected at the recommended dose of thiencarbazone-methyl·isoxaflutole application. The residue of isoxaflutole (one of the effective ingredients of thiencarbazone-methyl·isoxaflutole) directly and more strongly affected the diversity of soil bacterial communities than thiencarbazone-methyl. Increasing soil pH was recognised as an important factor in improving the diversity and structure of soil microflora based on the results of the Mantel test and canonical correspondence analysis. Supplemental use of nitrapyrin or modified attapulgite was found to increase soil pH, and further improve the expression of "manganese oxidation" function annotation. This contributed to the increased bacterial diversity (Shannon index). Therefore, the disturbance of soil microflora caused by thiencarbazone-methyl·isoxaflutole application can be mitigated by the use of nitrapyrin and modified attapulgite through raising soil pH.