Land use in urban areas impacts the composition of soil bacterial communities involved in nitrogen cycling. A case study from Lefkosia (Nicosia) Cyprus

The influence of wet-to-dry season shifts on the microbial community stability and nitrogen cycle in the Poyang Lake sediment

In lake environments, seasonal changes can cause exposure of the lake sediment, leading to soil formation. Although previous studies have explored how environmental changes influence microbial functioning in the water-level-fluctuating zone, few studies have investigated how wholescale habitat changes affect microbial composition, community stability and ecological functions in lake environments. To address this issue, our study investigated the effects of sediment-to-soil conversion on microbial composition, community stability and subsequent ecological functioning in Poyang Lake, China. Our results revealed that, during sediment-to-soil conversion, the number of total and unique operational taxonomic units (OTUs) decreased by 40 % and 55 %, respectively. Moreover, sediment-to-soil conversion decreased the microbial community connectivity and complexity while significantly increasing its stability, as evidenced by increased absolute values of negative/positive cohesion. In sediment and soil, the abundance of dominant bacteria, and bacterial diversity strongly affected microbial community stability, although this phenomenon was not true in water. Furthermore, the specific microbial phyla and genes involved in the nitrogen cycle changed significantly following sediment-to-soil conversion, with the major nitrogen cycling processes altering from denitrification and dissimilatory nitrate reduction to ammonium to nitrification and assimilatory nitrate reduction to ammonia. Moreover, a compensation mechanism was observed in the functional genes related to the nitrogen cycle, such that all the processes in the nitrogen cycle were maintained following sediment-to-soil conversion. The oxidation-reduction potential strongly affected network complexity, microbial stability, and nitrogen cycling in the sediment and soil. These results aid in the understanding of responses of microorganisms to climate change and extreme drought. Our findings have considerable implications for predicting the ecological consequences of habitat conversion and for ecosystem management.

Impact of anthropogenic land uses on soil microbiological activity in a peri-urban landscape

Land use and land cover patterns impact soil properties and negatively affect soil microbial community and related processes. However, the information regarding the influence of urban land use on soil microbial composition and functioning is limited. Here, we investigated the impact of urban land use patterns on soil microbiological parameters by comparing five contrasting anthropogenic land use classes, i.e. agriculture, park, roadside plantation, street green, and bare land. Soil physicochemical properties, basal respiration (BR), microbial biomass carbon (MBC), and enzyme activities were estimated and correlated. The results revealed that soil physicochemical and microbiological properties greatly varied across the five land use classes. Among all the land use types, the roadside plantation had the highest nutrient content, i.e. soil organic carbon (SOC), total nitrogen (TN), and mineral nitrogen (MN) (1.33%, 0.13%, 84.0 mg kg-1, respectively), while the soil functional capacities measured in terms of BR, MBC, microbial quotient (QCO2), soil microbial activity (SMA), and dehydrogenase activity (DHA) (9.90 C µg g-1 h-1, 300 µg g-1, 0.045 µg h-1/ µg MBC, 9.0 µg ml-1, 1.30 TPF g-1 h-1, respectively) were highest in the park. Disturbed street greens were markedly nutrient depleted and apparently exhibited lower microbial activity. Variations in soil BR, MBC, and enzyme activity were revealed to be primarily influenced by soil moisture, available phosphorus, and SOC content. We concluded that the negative impacts of anthropogenic land use soil quality and microbiological functioning can be managed by integrating proper management approaches for various land use classes in urban systems.

Different types of land use influence soil physiochemical properties, the abundance of nitrifying bacteria, and microbial interactions in tropical urban soil

Anthropogenic activities have led to unexpected changes in microbial community composition and structure, resulting in an interruption of soil ecological roles in urban environments. We questioned the impact of the different land use (e.g., agricultural, industrial, recreational, coastal, and residential areas) on the distribution of nitrifying bacteria and microbial interaction in tropical soil. The dominant nitrifying bacteria were ammonia-oxidizing archaea (AOA) in tropical soils up to 10⁷ copies/g of soil, while the abundance of ammonia-oxidizing bacteria (AOB) was significantly higher in agricultural soil only. Comammox (CMX) was ubiquitous up to 10⁵ copies/g of tropical soil, indicating that CMX might share ecological niches with AOA and considerably contribute to nitrification in urban areas. The most abundant phylum is Actinobacteria, accounting for 27-34 % relative abundance among most land-use types, but Proteobacteria was observed as the most prevalent phylum in agricultural soil. The physicochemical properties (e.g., soil pH and nutrient contents) of different types of land use influenced microbial richness and diversities associated with nitrogen cycling. Multivariate analysis disclosed that agricultural soils were distinct from other land uses because of the concentrations of nutrients and heavy metals and the abundance of microorganisms associated with nitrogen cycles. Also, the microbial co-occurrence network revealed that agricultural soils were a highly interconnected network of the microbial community. In this study, C: N ratio might have a significant impact on ecological networks and the abundance of nitrogen-related taxa, which could influence microbial interactions and complexity in tropical soils. Thus, the impact of anthropogenic land use induced changes in microbial composition and diversity, co-occurrence network, and nitrifying bacteria, leading to potential transformation in ecological services of tropical soils and nitrogen cycling in urban environments.

Which soil microbiome? Bacteria, fungi, and protozoa communities show different relationships with urban green space type and use-intensity

Exposure to diverse microbial communities early in life can help support healthy human immune function. Soil microbiomes in public and private urban green spaces are potentially important sources of contact with diverse microbiomes for much of the global population. However, we lack understanding of how soil microbial communities vary across and within urban green spaces, and whether these patterns vary across microbial kingdoms; closing this knowledge gap may help us optimise green spaces' capacities to provide this ecosystem service. Here we explore the diversity and community compositions of soil microbiomes across urban green space types in Tasmania, Australia. Specifically, we analysed soil bacterial, fungal, and protozoan diversity and composition across private backyards and public parks. Within parks, we conducted separate sampling for areas of high and low intensity use. We found that: (i) bacteria, fungi, and protozoa showed different patterns of variation, (ii) bacterial alpha-diversity was lowest in low-intensity use areas of parks, (iii) there was relatively little variation in the community composition across backyards, and high and low intensity-use park areas and (iv) neither human-associated bacteria, nor potential microbial community function of bacteria and fungi differed significantly across green space types. To our knowledge, this is the first urban soil microbiome analysis which analyses these three soil microbial kingdoms simultaneously across public and private green space types and within public spaces according to intensity of use. These findings demonstrate how green space type and use intensity may impact on soil microbial diversity and composition, and thus may influence our opportunity to gain healthy exposure to diverse environmental microbiomes.

Soil microbial communities shift along an urban gradient in Berlin, Germany

The microbial communities inhabiting urban soils determine the functioning of these soils, in regards to their ability to cycle nutrients and support plant communities. In an increasingly urbanized world these properties are of the utmost importance, and the microbial communities responsible are worthy of exploration. We used 53 grassland sites spread across Berlin to describe and explain the impacts of urbanity and other environmental parameters upon the diversity and community composition of four microbial groups. These groups were (i) the Fungi, with a separate dataset for (ii) the Glomeromycota, (iii) the Bacteria, and (iv) the protist phylum Cercozoa. We found that urbanity had distinct impacts on fungal richness, which tended to increase. Geographic distance between sites and soil chemistry, in addition to urbanity, drove microbial community composition, with site connectivity being important for Glomeromycotan communities, potentially due to plant host communities. Our findings suggest that many microbial species are well adapted to urban soils, as supported by an increase in diversity being a far more common result of urbanity than the reverse. However, we also found distinctly separate distributions of operational taxonomic unit (OTU)s from the same species, shedding doubt of the reliability of indicator species, and the use of taxonomy to draw conclusion on functionality. Our observational study employed an extensive set of sites across an urbanity gradient, in the region of the German capital, to produce a rich microbial dataset; as such it can serve as a blueprint for other such investigations.

Responses of Bacterial Taxonomical Diversity Indicators to Pollutant Loadings in Experimental Wetland Microcosms

Urbanization results in higher stormwater loadings of pollutants such as metals and nutrients into surface waters. This directly impacts organisms in aquatic ecosystems, including microbes. Sediment microbes are known for pollution reduction in the face of contamination, making bacterial communities an important area for bioindicator research. This study explores the pattern of bacterial responses to metal and nutrient pollution loading and seeks to evaluate whether bacterial indicators can be effective as a biomonitoring risk assessment tool for wetland ecosystems. Microcosms were built containing sediments collected from wetlands in the urbanizing Pike River watershed in southeastern Wisconsin, USA, with metals and nutrients added at 7 day intervals. Bacterial DNA was extracted from the microcosm sediments, and taxonomical profiles of bacterial communities were identified up to the genera level by sequencing 16S bacterial rRNA gene (V3–V4 region). Reduction of metals (example: 90% for Pb) and nutrients (example: 98% for NO3−) added in water were observed. The study found correlations between diversity indices of genera with metal and nutrient pollution as well as identified specific genera (including Fusibacter, Aeromonas, Arthrobacter, Bacillus, Bdellovibrio, and Chlorobium) as predictive bioindicators for ecological risk assessment for metal pollution.