The PhD thesis is devoted to the study of floristic and taxonomic diversity of diatoms from water bodies of the territory of Poltava-Plain algofloristic district (PPAD), its ecological and geographical characteristics, typological distribution, and sozological features.
As a result of our research, 601 species (629 infraspecific taxa) of diatoms that belonging to 4 classes, 17 orders, 38 families, and 87 genera, were registered in PPAD. The total number of taxa (literature and original data together) is 706 species (757 i.t.). It was identified that 392 species (402 i.t.) are new finds for the PPAD territory, 185 (192 i.t.) of which are new for the flora of Ukraine, 269 (277 i.t.) are new for the Forest-Steppe of Ukraine, 319 (327 i.t.) fre new for the Left-Bank Forest-Steppe zone.
Bacillariophyceae has the highest number of species. Its representatives dominate at the level of orders, families, and genera.
Species composition of diatoms from different types of water bodies of PPAD is varying. The highest number of species was found in rivers (584 species/ 612 i.t.), and the smallest in ponds (260/ 267), oxbow lakes (238/ 241), and swamps (232/ 234). The Vorskla River has the highest number of species (461/ 481), and the lowest number – in the Pond 2 (23 species.). The originality and typological species specificity were indicated: 220 taxa were found in rivers only, 6 – in swamps, 4 – in ponds, and 3 – in oxbow lakes. Comparative analysis of diatoms from different types of water bodies showed that the species composition of stagnant water bodies are the most similar to each other and was included in the flora of rivers, which is the richest in the number of species. This feature is associated with the location of these water bodies, as they all belong to the basins of the studied rivers.
It was found that cosmopolitian species are predominant in the studied area (66.9%). However, they are not indicators of species biogeographical distribution (Proshkina-Lavrenko, 1963). Therefore, the studied region obviously has the most favorable conditions for the Holarctic species. The distribution of diatoms among ecotopes is not uniform. The periphyton (93.8%) has the most diverse composition, slightly less species richness is typical for benthos (82.1%), and plankton (80.1%). Marked that 59, 17, and 10 species are characteristic exclusively of periphyton, benthos, and plankton, respectively. Among the identified halobility indicator taxa indifferent species (68.4%) were predominant, which is typical for freshwaters reservoirs. The number of halophilic species (27.6%) correlates with the hydrochemical features of PPAD territory (Vinarchuk, Khilchevsky, 2010). Among the species, which are indicators of water pH, alkaliphilic species are the most numerous (52.5%). This shows the alkalinization of PPAD waters. In relation to the trophic state of waters, oligo-mesotrophic (31.7%) and meso-eutrophic (33.3%) species are dominant, which indicates a mesotrophic type of PPAD water bodies. The predominance tolerant, sensitive to pollution species and species typical to the oligosaprobic and beta-mesosaprobic zone, indicate that PPAD water bodies belong to the II-III classes of water quality. (Rakowska, 2001; Barinova et al., 2019).
Analysis of morphological variability series of taxa, for the first time noted for the flora of Ukraine, allowed expanding our knowledge concerning their morphology, ecological characters, and distribution. In addition, for two species new nomenclature-taxonomic combinations were proposed: Surirella hibernica (W. Smith) D. Kapustin et O. Kryvosheia and Iconella amphioxys (W. Smith) D. Kapustin et O. Kryvosheia (Kryvosheia, Kapustin, 2019 b).
Algosozological analysis of the identified species list of PPAD showed that 17 species have the «endangered» sozological status of, 31 – are «vulnerable», 30 – are «rare», and 7 – are «data dificient taxa». Conditionally «rare» taxa are also noted, for which only a few (up to 5) locations are known in Ukraine and in the world: 102 species (104 i.t.) and 69 (72 i.d.) respectively. In addition, 539 species (563 i.t.) of diatoms were found in protected areas located on the territory of PPAD. The National Nature Park «Getmansky» has the highest number of species (376/ 388 i.t.), and the lowest number of species was found in the botanical reserve «Malopereshchepynsky» (112/ 113 i.t.).
The expediency of PPAD boundaries was established based a comparative analysis of the diatom flora of geographical areas included in it is structural parts. The comparison of the PPAD diatom flora with neighboring territories showed a certain similarity of the systematic structure of the studied floras and their originality. The diatom flora of the study region forms a group of similarity with the flora of the Kyiv Upland region, Belarus, and Poland. It can be a consequence of their close territorial location and purposeful study of Bacillariophyta of the lotic systems.
