Monika Tarkowska-Kukuryk

Diurnal dynamics of the microbial loop in peatlands: structure, function and relationship to environmental parameters

The interactions between bacteria and heterotrophic protists are essential for the ecosystem ecology of peatlands. We tested the hypothesis that fertility of a habitat may significantly influence the diurnal dynamics of the abundance of individual components of the microbial loop, as well as the number and intensity of correlations between bacteria and heterotrophic protists. Samples were taken in raised and carbonate peat bogs in three seasons, four times a day: at dawn, at noon, at dusk and at night. The results indicate that microbial community responses to physical and chemical parameters are complex but dependent on peatlands’ type and variable among microbes. Concentrations of nutrients may significantly influence the diurnal dynamics of the microbial communities. The most significant correlations occurred in the afternoon. At that time, the number and biomass of metabolically active bacteria correlated to the highest degree with concentrations of dissolved organic carbon, while in the evening, a clearly positive correlation between the abundance of bacteria and protists was observed. In a carbonate fen, the correlations were significantly weaker. Such knowledge will provide a more comprehensive understanding of the implication of chemical disturbance on microbial functions in relation with nutrient and carbon dynamics.

Diet composition of epiphytic chironomids of the Cricotopus sylvestris group (Diptera: Chironomidae) in a shallow hypertrophic lake

The diet composition of epiphytic Cricotopus sylvestris group larvae (Chironomidae) was examined for two size classes (<5 mm and 5–10 mm) from April to December in a shallow hypertrophic lake in eastern Poland. The C. sylvestris group dominated the epiphytic midge community on stems of Phragmites communis, accounting for 90–96% of the total population by number. The diet of both size classes of this midge consisted mostly of detritus and associated protozoa to the exclusion of many other potential food choices, such as epiphytic algae (chlorophytes, diatoms, filamentous green algae Cladophora sp.) numerously present in this microhabitat.

Effects of rotifers, copepods and chironomid larvae on microbial communities in peatlands

Interactions between the microbial loop and the classical grazing food chain are essential to ecosystem ecology. The goal of the present study was to examine the impact of chironomid larvae, rotifers and copepods on the major components of the microbial food web (algae, bacteria, heterotrophic flagellates, testate amoebae and ciliates) in peatlands. Two enclosure experiments were carried out in a Sphagnum peatland. In the experiments we manipulated rotifers, copepods and macroinvertebrates, i.e. chironomid larvae (Psectrocladius sordidellus gr). During the experiments variation was observed in the abundance of potential predators. The beginning of the first experiment was distinguished by dominance of rotifers, but five days later copepods were dominant. In the second experiment copepods dominated. The results of this study are the first to suggest a substantial impact of chironomid larvae, rotifers and copepods on microorganism communities in peatland ecosystems. The impact is reflected by both a decrease in the abundance and biomass of testate amoebae and ciliates and a transformation of the size structure of bacteria. Heterotrophic flagellates (HNF) were not controlled by metazoans, but rather by testate amoebae and ciliates, as HNF were more abundant in the control treatment.

Ecology of ciliates in microbial mats in meltwater streams, King George Island, maritime Antarctica

Microbial communities living in microbial mats are known to constitute early indicators of ecosystem disturbance, but little is known about their response to environmental factors in the Antarctic. This paper presents the first major study on ciliates from microbial mats in streams on King George Island (Antarctica). The objective of the study is to investigate the structure and spatial distribution of ciliate communities and to identify the environmental factors determining the structure of the assemblages. Additionally, we compared ciliate communities inhabiting streams on King George Island with other isolated islands of the maritime Antarctic. Samples of microbial mats for ciliate analysis were collected from three streams fed by Ecology Glacier. Sampling was carried out three times from 17 January to 24 February 2012. The total numbers of ciliates were dominated by small taxa recognized as cosmopolitan, also recorded on other islands of the maritime Antarctic. The species richness, abundance, and biomass of ciliates differed significantly between the stations studied, with the lowest numbers in the middle course of the stream and the highest numbers in the microhabitats closest to the glacier and at the site where the stream empties into the pond. Variables that significantly explained the variance in ciliate communities in the transects investigated were total organic carbon, total nitrogen, temperature, dissolved oxygen, and conductivity. Further research is required to explain the impact of biotic factors on the presence of ciliates, including the abundance of bacteria, microalgae, and small metazoa.

Effects of experimental addition of nitrogen and phosphorus on microbial and metazoan communities in a peatbog

Interactions between microbial communities and the classical grazing food chain are essential for understanding the functioning of peatbog ecosystems. However, little is known of how short-term intensification of eutrophication processes may influence microbial and metazoan communities in transitional peatbog. We addressed the hypothesis that an increase in the concentration of nutrients will affect the species richness and abundance of microorganisms and small metazoans and cause changes in the food web structure in a peatbog. The experiments were performed in a transitional peatbog. Four experimental variants were conducted (control and nutrient-enriched: +P, +N and P+N). Increased habitat fertility was found to modify the taxonomic composition and functioning of microbial communities. We observed a strong reduction in the species richness of testate amoebae-top predators, and a substantial increase in the abundance of bacteria, flagellates and ciliates. A better understanding of which parameters regulate microbial populations in peatbogs is critical for more accurate prediction of how peatbogs will respond to global climate change or anthropogenic disturbances.