DIATOMS FROM A PEAT BOG ON THE PEŠTER PLATEAU ( SOUTHWESTERN SERBIA ) : NEW RECORDS FOR DIATOM FLORA OF SERBIA

The distribution of diatoms was studied in three types of diatom communities (epiphytes, benthos and plankton) of a peat bog on the Pešter plateau. The observed diatom flora inhabited all investigated communities, comprising in total 250 taxa in 53 genera. Among them, 45 taxa were new records for the Serbian diatom flora. Identified taxa belonged to different groups of algae, however alkaliphile diatoms were dominant. New ecological data for Encyonopsis minuta, Pinnularia isostauron and P. marchica are presented here. All the diatoms were documented by light micrographs, and brief notes on their morphology, distribution and ecology are provided.


INTRODUCTION
Among aquatic ecosystems, peat bogs are a very specific environment, possessing unique ecological properties and remarkably high diversity of diatom flora.In Serbia, they are not as numerous as in northern and western Europe.In addition, they are gradually disappearing due to anthropogenic and climatic factors (Buczko and Wojtal, 2005;Kulikovskiy et al., 2010;Šovran et al., 2013).These factors mutually affect the composition of the total algal flora, including diatom flora, which is a permanent component of the biota in peat bogs (Kulikovskiy, 2008).
The main purpose of the study was to record the floristic characteristics of the diatom assemblages of the peat bog on the Pešter plateau due to its uniqueness not only in Serbia but in Europe as well.There are relatively little literature data about the morphology, distribution and ecology of diatoms from the peat bog on the Pešter plateau (Krizmanić, 2009;Vidaković et al., 2013).

Description of the study area
The Pešter plateau is located in southwestern Serbia and lies at an altitude of 1150-1492 m a.s.l.With an area of around 50 km², Pešter is the largest plateau in Serbia, and the highest on the Balkan Peninsula.Four rivers (Uvac, Vapa, Jablanica and Grabovica) flow through the plateau.The peat bog from the Pešter plateau is one of the last large preserved peat bogs in Serbia.It has a somewhat acid reaction, with a fair amount of organic matter, but with humic acids predominating (Tešić et al., 1960).

MATERIALS AND METHODS
The study was based on 29 samples collected in June and September 2008, May 2009 and August 2011 from three localities (Fig. 1).Epiphytic samples were collected by squeezing out or scraping off dominant submerged macrophytes and mosses.Samples of phytobenthos were collected with a pipette from the surface of the bottom deposits.Phytoplankton samples were collected by towing a plankton net (Ø 25 μm) through the open water.All samples were fixed with formaldehyde to a final concentration of about 4% shortly after sampling.
Water temperature and transparency were measured in situ at all localities.Water samples for chemical analysis were collected using a Ruttner sampler (depth 0.5 m).The samples were stored in plastic containers at 4 o C for transfer to the laboratory for further analyses.The analysis of physicochemical parameters of water (pH, conductivity, Ca 2+ concentrations) was performed at the Institute of Public Health of Serbia "Dr Milan Jovanović Batut", by standard analytical methods.
In laboratory algological samples were treated using standard methods to obtain permanent slides of diatoms (Krammer and Lange-Bertalot, 1986).Light microscope observations and micrographs were made using a Zeiss AxioImagerM.1 microscope with DIC optics and AxioVision 4.8 software.

Physical and chemical parameters
The results of the physical and chemical parameters of water are summarized in Table 1.The peat bog on the Pešter plateau differed in physicochemical parameters from peat bogs such as the sphagnum bogs of the Volga Upland (Kulikovskii, 2008), Nur bog in northern Mongolia (Kulikovskii et al., 2010) or peat bogs in the Mari-time Alps Nature Park (Falasco and Bona, 2011).The pH was significantly lower in the sphagnum bogs of the Volga Upland (4.4-5.1) and in Nur bog (5.5-5.6), but in the Maritime Alps Nature Park the pH was similar to our values (6.17-6.68).The conductivity range was much higher than in other peat bogs, sphagnum bogs of the Volga Upland (27.3-54 µS cm -1 ), peat bogs in the Maritime Alps Nature Park (17-26 µS cm -1 ).

Stauroneis separanda
The flora of diatoms from the peat bog on the Pešter plateau is formed of acidobiontic, acidophiles, neutrophiles, alkaliphiles, alkalibiontic, indifferents, aerophilic and widely distributed taxa.It is based on the ecological characteristics of taxa according to Lecointe et al. (1993) and Van Dam et al. (1994).Among them, alkaliphile diatoms were dominant.The large development of alkaliphilic species is evidently related to an insufficient study of acidic habitats, including peat bogs (Kulikovskiy, 2008).
The ecological characteristics of the new observed taxa presented in this text, are matched with literature data, with several exceptions.This is a contribution to the knowledge of ecological data for Encyonopsis minuta, because of the lack of differentiation within the Cymbella microcephala complex (Hofmann et al., 2013).In our samples, Pinnularia isostauron was observed at higher pH values than recorded in the literature (pH of 6 and less), while P. marchica was recorded at lower pH values and at lower conductivity values than suggested by literature data (pH from 7.5-8.8and conductivity about 800 µS cm -1 ) (Krammer, 2000).
Species composition and distribution in the Pešter plateau peat bog, according to Lecointe et al. (1993) and Van Dam et al. (1994), indicate the dystrophic, oligotrophic up to mesotrophic environment of the peat mound.On the whole, the flora is formed by cosmopolitan species with a large involvement of taxa from alpine and subalpine areas.

Table 1 .
Ranges of physical and chemical parameters at peat bog localities of the Pešter plateau.

Table 2 .
Checklist of the 45 new observed taxa for Serbian diatom flora from the peat bog at Pešter plateau.
*In the material studied it occurred as a single specimen and will not be described in this paper.B − benthos, EP − epiphytes, P − plankton NEW RECORDS FOR DIATOM FLORA OF SERBIA