Effects of fires on vascular plant and microalgae communities of steppe ecosystems

The article is focused on a hypothesis verification: the higher plants, microalgae and cyanobacteria may be used in bioindication of steppe ecosystem restoration dynamics after fires. On the territory of the Askania Nova biosphere reserve (Ukraine) 4 stationary polygons were investigated: SP1 – steppe area which had not been exposed to fire for 20 years preceding our study, as well as areas where single fires occurred in 2001 (SP2), 2005 (SP3), and a site where fires occurred in 2001 and 2004 (SP4). The investigation revealed the dynamics of height and projected area of the higher vegetation according to seasons during two years (2010 and 2011), as well as abundance and biomass of microalgae and cyanoprokaryotes in the soil layer by the layer of the depth to 15 cm. It was found that the effects of pyrogenic load remain evident for several years after the fires, manifesting in decrease of the height and projected area of herbage, the number and biomass of algae and cyanobacteria in the soil, especially to the depth of 5 cm. Multivariate general linear models were used to test the significance of the dependence of quantitative characteristics of vegetation, microalgae, and cyanoprokaryotes on environmental predictors (season, year, soil layer, and fire). In the model, 75.2% of the grass height variability and 91.6% of the grass projected area variability could be explained by the predictors under consideration. In the series SP1 → SP2 → SP3 → SP4 the grass height and projected area decreased. The differences in the projected area of the grass stand were most evident in spring. The model explained 89.1% of the variation in abundance and 91.6% of the variation in biomass of Bacillariophyceae. The abundance of Bacillariophyceae was greater in the upper soil layer than in the lower layer and decreased with depth. The abundance of this group of algae decreased in the series SP1 → SP2 → SP3 → SP4 at depths of 0–5 and 5–10 cm. Changes in abundances of Chlorophyta, Streptophyta, Heterokontophyta (Xanthophyceae and Eustigmatophyceae) equaling 47.6% could also be explained by the model. The abundance of this group of algae was greatest in the upper soil layer. In the upper soil layer, the maximum abundance of Chlorophyta, Streptophyta, and Heterokontophyta (Xanthophyceae and Eustigmatophyceae) was recorded for Polygon SP1 and the minimum for Polygon SP3. Within the model, 48.0% of the variation in biomass of Chlorophyta, Streptophyta, and Heterokontophyta (Xanthophyceae and Eustigmatophyceae) was explained by the environmental predictors. The biomass trend was coherent with the population trend. A special feature was that there was a significant increase in biomass at 10–15 cm depth at Polygon SP3 compared to other polygons at this depth. The model was able to explain 61.8% of the variation in abundance and 66.7% of the variation in cyanobacteria biomass. The highest abundance of cyanobacteria was found in the upper soil layer of polygon SP1. Somewhat lower numbers of cyanobacteria were at polygons SP2 and SP4, and the lowest were found in the upper soil layer at polygon SP3. In turn, the highest number of cyanobacteria was found particularly at this polygon in the 5–10 cm layer. The biomass in the 0–5 cm layer was coherent with the abundance pattern of this group. The research results confirmed that the quantitative characteristics of the higher vegetation (height and projected area) as well as of microalgae and cyanobacteria (abundance and biomass) may be used in bioindication of the dynamics of post-pyrogenic processes in steppe ecosystems.

Use of soil biota in the assessment of the ecological potential of urban soils

In assessing the ecological conditions and classification of urban soils, data about soil biota should be taken into account. The environment of urban territories is characterized by significant changes compared to their surrounding environments. It is established that the algal flora of urban soils lose their zonal features and features associated with the edification influence of higher plants. Specific biotopes with a definite species structure are formed in urboecosystems. Fifty 50 algae species have been recorded in the soils of the Henichesk urboecosystems (Kherson region, Ukraine): Cyanoprocaryota – 21, Chlorophyta – 13, Charophyta – 2, Eustigmatophyta – 1, Xanthophyta – 11, Bacillariophyta – 2. Among dominant and subdominant species were Cyanoprocaryota and Chlorophyta. The other phyla were represented by Klebsormidium dissectum, K. flaccidum, Hantzschia amphioxys, Eustigmatos magnus, Botrydiopsis eriensis. Compared with the surrounding environment, the urbanized flora of Henichesk has a low species richness, and is characterized by prevalence of Cyanoprocaryota and Chlorophyta species. The coefficient that takes into account the percentage of preservation of species richness in a particular urban area compared to the background indicators of species richness can be used to evaluate the urban transformation of soil biota. The degree of degradatory changes in the composition of living organisms and the direction of these changes depends on the specificity and intensity of exploitation of the territory of the urban ecosystem. The most diverse composition of algae species within the the city of Henichesk was noted in the recreational, residential, and transport zones, in comparison with the industrial zone and the zone of special use. Different functional areas of the city are distinguished not only by the algae species richness, but also by the composition of dominants. Among the dominants and subdominants of the recreational and transport zones were species of different phyla. The dominants and subdominants of the residential and industrial zones were Cyanoprocaryota species, in the zone of special use – representatives of Chlorophyta. The distribution of species richness of algae along the soil profile in the city acquires an atypical character. The species richness increases not in the most superficial layers of soil, but in the lower, aphotic parts of the soil profile. The soil biota, on the one hand, depends on the ecological conditions of soil, and on the other as a result of its life activity, changes the ecological functions of the soil, strengthening or weakening them. The reduction in the species richness of the soil algae of the urboecosystem Henichesk shows the limitations of ecological functions of urban soils. It is established that changes in the composition of algae in soils of urban ecosystems are one of the indicators of the presence and severity of transformation processes. These processes occur with the soil biota and soil as a whole under the conditions of urban ecosystems and can be used as indicators in the environmental assessment of urban soils, in the development and subsequent examination of ways to reduce negative expression of urbanization.

Post-pyrogenic changes in vegetation cover and biological soil crust in steppe ecosystems

The study of the processes of restoration of species richness and productivity of steppe ecosystems after fires is an urgent problem that affects not only the conservation of biodiversity but also the maintenance of pasture resources. This article presents the results of a study of post-pyrogenic effects in steppe ecosystems, taking into account changes in the species composition of cyanoprokaryotes and algae that are art of the biological soil crust, which performs ecologically important functions in xerophytic ecosystems. The investigations were carried out in virgin and post-pyrogenic steppe ecosystems of the “Troitsk Clough” reserve (Zaporizhia region, Ukraine). For three years, the dynamics of the projective cover and the height of the vegetation cover in virgin areas of herbs-fescue-feather-grass and fescue-feather-grass steppes was studied as well as within two ecosystems of post-pyrogenic development after fires that occurred in the spring and winter periods. We discovered that restoration of the herbs-fescue-feather-grass and fescue-feather-grass steppes after fires occurs at different rates. The cause of the slow restoration of vegetation cover can be its severe damage by fire at the beginning of the vegetation season and the development of erosion processes. The number of species of cyanoprokaryotes and algae in the biological soil crust of virgin and post-pyrogenic ecosystems is not significantly different. It varies from 35 to 49 species. The greatest diversity is noted for Cyanoprokaryota. Chlorophyta is in the second place. Among the dominants, the filamentous forms of Cyanoprokaryota prevail. Nostoc edaphicum was noted as a nitrogen fixing representative. The similarity of the species lists of cyanoprokaryotes and algae of post-pyrogenic and virgin ecosystems, according to the calculated Jaccard coefficient, varies from 49.1% to 55.3%. This indicates a strong specificity of the composition of cyanoprokaryotes and algae in post-pyrogenic biological soil crusts. Changes in their composition reflect different stages of post-pyrogenic succession. In the first year after a fire, there is a slight increase in species richness, which is a consequence of the favorable effect of increasing the amount of mineral substances in the soil after the organic matter has burned out. The “pioneer” group includes: Phormidium autumnale, Ph. dimorphum, Ph. retzii, Ph. (Leptolyngbya) henningsii, Luticola mutica, Hantzschia amphioxys. Gradually this effect is leveled and the species richness of cyanoprokaryotes and algae is stabilized at a level peculiar for this type of ecosystem. 

Exposure of human corneal epithelial cells to contact lenses in vitro suppresses the upregulation of human β-defensin-2 in response to antigens of Pseudomonas aeruginosa

Bacterial keratitis is a sight-threatening complication of contact lens wear, and Pseudomonas aeruginosa is a commonly isolated pathogen. The mechanisms by which lenses predispose the cornea to P. aeruginosa infection are unknown. Corneal epithelial cells express numerous innate defenses, some of which have bactericidal effects against P. aeruginosa. One of these is human beta-defensin-2 (hBD-2), which is upregulated in response to lipopolysaccharide or flagellin antigens. We hypothesized that prior exposure of corneal epithelia to a contact lens would interfere with upregulation of hBD-2 in response to P. aeruginosa. A novel in vitro model was used in which cultured human corneal epithelial cells were exposed to a hydrophilic contact lens for up to 3.5 days prior to challenge with a culture supernatant of P. aeruginosa antigens for 6h. Without prior lens exposure, the supernatant caused >2-fold upregulation of hBD-2 mRNA message and expression of hBD-2 peptide. Prior contact lens exposure blocked this upregulation without obvious effects on cell health. Western immunoblot and luciferase reporter studies showed that Pseudomonas-induced hBD-2 upregulation involved MyD88, c-Jun N-terminal kinase and both AP-1 and NF-kappaB transcription factors. Contact lenses did not affect surface expression of Toll-like receptor-2, -4 or -5, but did block antigen activation of AP-1, but not NF-kappaB, transcription factors. These data show that contact lenses can interfere with epithelial defense responses to bacterial antigens in vitro, and if translated in vivo, could help predispose the cornea to infection.