Short-term impacts of polyethylene and polyacrylonitrile microplastics on soil physicochemical properties and microbial activity of a marine terrace environment in maritime Antarctica

Evidence of microplastic (MP) pollution in Antarctic terrestrial environments reinforces concerns about its potential impacts on soil, which plays a major role in ecological processes at ice-free areas. We investigated the effects of two common MP types on soil physicochemical properties and microbial responses of a marine terrace from Fildes Peninsula (King George Island, Antarctica). Soils were treated with polyethylene (PE) fragments and polyacrylonitrile (PAN) fibers at environmentally relevant doses (from 0.001% to 1% w w-1), in addition to a control treatment (0% w w-1), for 22 days in a pot incubation experiment under natural field conditions. The short-term impacts of MPs on soil physical, chemical and microbial attributes seem interrelated and were affected by both MP dose and type. The highest PAN fiber dose (0.1%) increased macro and total porosity, but decreased soil bulk density compared to control, whereas PE fragments treatments did not affect soil porosity. Soil respiration increased with increasing doses of PAN fibers reflecting impacts on physical properties. Both types of MPs increased microbial activity (fluorescein diacetate hydrolysis), decreased the cation exchange capacity but, especially PE fragments, increased Na+ saturation. The highest dose of PAN fibers and PE fragments increased total nitrogen and total organic carbon, respectively, and both decreased the soil pH. We discussed potential causes for our findings in this initial assessment and addressed the need for further research considering the complexity of environmental factors to better understand the cumulative impacts of MP pollution in Antarctic soil environments.

Microbial successional pattern along a glacier retreat gradient from Byers Peninsula, Maritime Antarctica

The retreat of glaciers in Antarctica has increased in the last decades due to global climate change, influencing vegetation expansion, and soil physico-chemical and biological attributes. However, little is known about soil microbiology diversity in these periglacial landscapes. This study characterized and compared bacterial and fungal diversity using metabarcoding of soil samples from the Byers Peninsula, Maritime Antarctica. We identified bacterial and fungal communities by amplification of bacterial 16 S rRNA region V3-V4 and fungal internal transcribed spacer 1 (ITS1). We also applied 14C dating on soil organic matter (SOM) from six profiles. Physico-chemical analyses and attributes associated with SOM were evaluated. A total of 14,048 bacterial ASVs were obtained, and almost all samples had 50% of their sequences assigned to Actinobacteriota and Proteobacteria. Regarding the fungal community, Mortierellomycota, Ascomycota and Basidiomycota were the main phyla from 1619 ASVs. We found that soil age was more relevant than the distance from the glacier, with the oldest soil profile (late Holocene soil profile) hosting the highest bacterial and fungal diversity. The microbial indices of the fungal community were correlated with nutrient availability, soil reactivity and SOM composition, whereas the bacterial community was not correlated with any soil attribute. The bacterial diversity, richness, and evenness varied according to presence of permafrost and moisture regime. The fungal community richness in the surface horizon was not related to altitude, permafrost, or moisture regime. The soil moisture regime was crucial for the structure, high diversity and richness of the microbial community, specially to the bacterial community. Further studies should examine the relationship between microbial communities and environmental factors to better predict changes in this terrestrial ecosystem.

The Impact of Constrictotermes cyphergaster (Termitidae: Nasutitermitinae) Termites on Semiarid Ecosystems in Brazil: A Review of Current Research

Termites have global distributions and play important roles in most ecosystems, often with high nest densities and interesting associations with other organisms. Constrictotermes cyphergaster, is a termite endemic to South America, widely distributed and very conspicuous, and has therefore been considered a good model for filling in gaps in general termite ecology and their relationships with other organisms (e.g., termitophily). A systematic review (content and bibliometric analyses) was used to gather all published scientific knowledge related to C. cyphergaster as well as to observe trends, verify gaps, and direct new perspectives for future studies of this species. We identified 54 studies, of which more than 50% were published in the last five years (28 articles). The majority of the articles investigated the relationships between C. cyphergaster and macroorganisms (44.4%), followed by specific aspects of its biology (25.9%). The collaboration network revealed that links between researchers are still limited and modular, but trending topics have changed over time. Additionally, there are differences in the aims of the studies being carried out in the Caatinga and Cerrado domains, with some information focusing only on one of those environments. Our results show that some gaps in the biology and ecology of C. cyphergaster remain to be explored, although collaborative efforts between researchers open opportunities for suggesting future studies that would make relevant contributions to the general knowledge of termites.

Solos e Evolução da Paisagem em Ambiente Periglacial na Península Barton, Antártica Marítima

As baixas disponibilidade de água líquida e temperatura na Antártica condicionam a formação de solos incipientes. Condições climáticas menos severas na Antártica Marítima permitem o maior desenvolvimento de solos, com maior cobertura vegetal e intemperismo químico mais significativo. A Península Barton, localizada na Ilha Rei George (Antártica Marítima), possui solos derivados de litologias diversas, com destaque para o basalto/andesito piritizado, representando a área de maior extensão de materias sulfídicos na região. O objetivo deste trabalho foi analisar o papel do relevo na gênese de solos sulfatados e sua relação com a evolução da paisagem. Os solos foram classificados de acordo com a Soil Taxonomy e WRB/FAO. Foram descritos três perfis em toposequência e analisados seus atributos morfológicos, físicos, químicos e mineralógicos. A crioclastia está presente como um processo pedogenético, mas o que se destaca é o grau evolutivo dos solos associado à acidificação pela oxidação dos sulfetos. Esse processo promove a liberação de elementos como o Fe, que são mobilizados por influência do relevo. Consequentemente, formam-se niveis encouraçados, isto é, horizontes petroplínticos, caracterizando uma transformação da cobertura pedológica. A gênese destes solos demonstra que a paisagem periglacial é dinâmica e de profundo interesse das investigações pedogeomorfológicas.

Geochemistry and spatial variability of metal(loid) concentrations in soils of the state of Minas Gerais, Brazil

Since 2009 a policy has been implemented in Brazil to establish the natural concentrations of potentially toxic substances in soil for each state. Historically a 'mining state', Minas Gerais established a Quality Reference Value for metal(loid)s for all of the soils in the state. To successfully establish these values it is important to study the spatial geochemical diversity for the state. In this context, the objectives of this work are: (1) to evaluate the natural concentrations of metal(loid)s in pristine Minas Gerais soils and (2) to interpret the spatial variability in concentration of these elements. The 0-20 cm layer of soils was sampled for 697 georeferenced sites including the main geological materials and soil groups. Soil properties were analyzed according to methodologies suitable for Brazilian soils. The concentration of metal(loid)s was determined by acid extraction according to EPA 3051A. Descriptive statistics, Pearson correlation and spatial variability analyses were performed. The dominance of acidic pH and low CEC values reflects the pervasive deep acid weathering. The variability of metal(loid) concentrations for soils of the state may be attributed to geological diversity and different pedogenesis. Correlation and spatial analysis indicated that the Fe concentration is strongly associated with metal(loid) concentrations in topsoil. According to the spatial geochemical diversity of the state, a k-means cluster analysis was performed which identified four clusters. A significant difference in the mean values of metal(loid) concentrations between the clusters confirmed that the single Quality Reference Value established does not represent the geochemical diversity of soils in Minas Gerais.