Richness, coverage and concentration of heavy metals in vascular epiphytes along an urbanization gradient

Isotopic composition (δ13C and δ15N) in the soil-plant system of subtropical urban forests

This study brings information on the dynamics of C and N in urban forests in a subtropical region. We tested the hypothesis that C and N isotopic sign of leaves and soil and physiological traits of trees would vary from center to periphery in a megacity, considering land uses, intensity of automotive fleet and microclimatic conditions. 800 trees from four fragments were randomly chosen. Soil samples were collected at every 10 cm in trenches up to 1 m depth to analyze C and N contents. Both, plants and soil were assessed for δ¹³C, δ¹⁵N, %C and %N. Physiological traits [carbon assimilation (A)], CO₂ internal and external pressure ratio (Pi/Pa) and intrinsic water use efficiency iWUE were estimated from δ¹³C and Δ δ¹³C in leaves and soil ranged from -27.42 ‰ to -35.39 ‰ and from -21.22 ‰ to -28.18 ‰, respectively, and did not vary along the areas. Center-periphery gradient was not evidenced by C. Emissions derived from fossil fuel and distinct land uses interfered at different levels in δ¹³C signature. δ¹⁵N in the canopy and soil varied clearly among urban forests, following center-periphery gradient. Leaf δ¹⁵N decreased from the nearest forest to the city center to the farthest, ranging from <3 ‰ to <-3 ‰. δ¹⁵N was a good indicator of atmospheric contamination by NO_x emitted by vehicular fleet and a reliable predictor of land use change. %N followed the same trend of δ¹⁵N either for soils or leaves. Forest fragments located at the edges of the center-periphery gradient presented significantly lower A and Pi/Pa ratio and higher iWUE. These distinct physiological traits were attributed to successional stage and microclimatic conditions. Results suggest that ecosystem processes related to C and N and ecophysiological responses of urban forests vary according to land use and vehicular fleet.

Urbanization significantly impacts the connectivity of soil microbes involved in nitrogen dynamics at a watershed scale

As one of the most dominant ecosystems of urban green space, turfgrasses provide a wide range of ecosystem services. However, little is known about the interactions of microbial communities in turfgrass soils and how these interactions respond to expanding development of impervious surfaces during watershed urbanization. In this study, we analyzed bacterial communities and their co-occurrence patterns in turfgrass soils along an urbanization gradient as measured by the proportion of impervious surfaces in Jiulong River watershed in Fujian, China. Results show that the diversity and network size of bacterial communities negatively associated with impervious surfaces. The bacterial communities showed non-random co-occurrence patterns, with more intra-module connections observed for urbanized networks. The co-occurrence network with distinct modules of soil samples with contrasting land cover imperviousness suggested different functional organizations with altered microbial nitrogen processes. Structural equation modelling revealed that watershed impervious surfaces had indirect impacts on microbial connectivity by altering soil properties, including pH, temperature, moisture, C/N and nitrate (NO₃^-). Moreover, impervious surfaces affected microbial connectivity far more than human population density. Our study highlights the significance of human disturbances in affecting microbial interactions and assemblies in turfgrass ecosystems through impervious surfaces and provides benefits for sustainable urban planning and management at a watershed scale.

Effect of urbanization on the micronucleus frequency in birds from forest fragments

The urbanization contributes to environment contamination, mainly by the increased vehicle traffic. This intense traffic releases in the air chemical compounds with mutagenic properties that can affect the entire ecosystem. The birds for the flight accumulate air, absorbing gases or particles. The absorption of this polluted air may be causative agent responsible for micronucleus (MN) induction in bird erythrocytes. The quantitative analysis of MN in birds can assists in the monitoring environmental quality of various places. The study aimed to quantify the MN frequency in birds and compare their variation: I) among forest fragments distant from and near to urbanization, II) among species and populations of birds and III) to find if there is a relation between vehicle traffic and MN induction. The capture of the birds took place in four forest fragments in central Brazil (two distant and two near the city) using mist nets. Blood smears were prepared with blood collected from the tarso-metatarsal vein. A total of 354 individuals were analyzed and MN were found in 52% of the individuals analyzed. All sampled birds were identified and resulted to belong to 50 different species, only 4 of which were captured in all the 4 forest fragments. The average MN frequency, regardless of bird species and sampling area, was 1.04/10,000 erythrocytes. From an overall analysis carried out on all birds, the MN frequencies were found to vary among forest fragments distant from and near to urbanization (x² =15.513; p < 0.001) and demonstrated positive correlation between vehicle traffic intensity and the MN frequency (r = 0.988; df=2; p = 0.011). The species of birds presented variation in the amount of MN (x² = 84.64; df=49; p = 0.001). Therefore, a restricted analysis carried out on the 4 species of birds present in all the forest fragments showed that the populations of Antilophia galeata (x² =6.029; p = 0.014), Basileuterus culicivorus (x² =9.53; p = 0.002), Eucometis penicillata (x² =8.067; p = 0.005) and Myiothlypis flaveola (x² =4.771; p = 0.029) showed difference in the MN frequency, when compared between forest fragments distant from and near to cities. The analysis demonstrated that birds living in forest areas near to the city presented higher MN frequency, probably because pollutants generated by urbanization affect birds and that the larger the vehicle traffic the greater the induced MN in the birds.

Morphophysiological variation and metal concentration in the thallus of Parmotrema tinctorum (Despr. ex Nyl.) Hale between urban and forest areas in the subtropical region of Brazil

Anthropic activities such as the emission of pollutants resulting from industrial and agropastoral activities promote several changes in urban and forest areas. Lichens are organisms that are used in air quality evaluations due to their sensitivity to these changes. The aim of this study is to analyze the presence of morphophysiological damages and the metal concentration in samples of the lichen Parmotrema tinctorum, in urban and forest areas, checking for possible parameter variations between these areas, in the different matrices and seasons in the Southern region of Brazil. Six areas were selected (urban and forest), assigned to the rural/urban and urban/industrial matrices belonging to the watershed of the Rio dos Sinos, Brazil. The following parameters were analyzed: Index of photobiont vitality (IPV), photosynthetic pigments (chlorophyll, carotene, and pheophytin) and metals (Cu, Cr, Zn, Pb, and Ni) in the thallus of the lichen. The data were analyzed by an ANOVA one way, Pearson correlation test, and principal component analysis (PCA). Variations in the morphophysiological parameters were recorded in all the areas revealing significant differences. The lowest IPV values and highest concentration of metals were recorded in the urban environment, while low chlorophyll levels were found in the forest areas. The PCA showed a distinction between the areas and the season. The level of urbanization, vehicle traffic, and the weather conditions might have influenced the results. The use of P. tinctorum, the index of photobiont vitality and chlorophyll and pheophytin content, has proved to be an efficient tool to diagnose the air quality in the areas analyzed, allowing its use as a model in air monitoring studies, both in urban and forest areas, as well as in distinct matrices in the subtropical region.

Comunidade de liquens corticícolas em um gradiente de urbanização na Bacia Hidrográfica do Rio dos Sinos, no sul do Brasil

Resumo Liquens são mundialmente conhecidos como indicadores de qualidade ambiental porque são sensíveis às modificações do ambiente, especialmente as de origem antrópica. Neste estudo foram avaliadas a riqueza, a composição e a cobertura de comunidades de liquens corticícolas em nove municípios com diferentes graus de urbanização e verificadas as principais semelhanças na composição das espécies entre as comunidades. Os locais amostrados estavam distribuídos em uma matriz rural, rural/urbana ou urbana/ industrial. Dez forófitos foram amostrados em cada área, utilizando o método do elástico. Ao total, foram identificadas 215 espécies de liquens, das quais nove são novas ocorrências, sendo quatro para o Brasil e cinco para o Rio Grande do Sul. Com o aumento da urbanização, observou-se uma simplificação da estrutura da comunidade de liquens, com diminuição da riqueza e mudanças na composição das espécies. Além disso, na matriz urbana/industrial poucas espécies apresentaram alta porcentagem de cobertura e, em conjunto, somaram grande importância na comunidade. Maior homogeneidade da composição de espécies foi encontrada em áreas mais próximas e inseridas na matriz urbano/industrial. Este estudo demonstrou que a arborização urbana é um fator importante para o estabelecimento das espécies de liquens, ao longo de um gradiente de urbanização.