Browsing by Subject "levä"

Viruses are a functional part of the water ecosystems microbial network. There is scientific evidence that viruses have impact to biotic communities, nutrient recycle and genetic diversity. Still there is a lack of studies concerning fresh water ecosystem viruses. In Finland, studies of fresh water viruses have not been published. Main objective of this thesis was to study, first time in Finland, abundance and variation of virus like particles (VLP) in boreal lake. The study was carried out on Lake Vesijärvi in Southern Finland. Purpose was also to study the abundance relations of VLP to bacterial abundance and algae biomass. Temporal changes of the variables were studied in 4 periods during growing season in 2007 and 2 periods during winter season in 2008. Spatial changes of variables were studied in littoral and pelagic zones in early summer 2007. Abundance of VLP was high in productive layer (11,9 ± 0,7 x 107 (ml-1)). Similar results have been observed from studies with other lakes in boreal zone. Highest abundance observed was in early summer period (14,9 ± 0,2 x 107 (ml-1)) and lowest at the end of the winter season period (5,5 ± 1,3 x 107 (ml-1)). High bacteria abundance and algae biomass with suitable physical and chemical conditions were the main reasons for high VLP abundance. In the growing season an average amount of chlorophyll –a was 8,6 μgl-1. In the winter season a very high amount of chlorophyll –a was observed (22,4 ± 1,2 μgl-1) indicating under ice algal bloom. Bacteria abundance was stable during the growing season (1,3 x 107 ml-1) corresponding to findings with earlier studies on Lake Vesijärvi. Virus / bacteria ratio (VBR) –level varied between 7,5 – 25,3 in the growing season and in the winter season between 1,6 - 9,3. Bacterial abundance growth explained 18,2 % of the growth of the VLP abundance (p=0,004, all periods included). In the growing season chlorophyll –a explained 17,4 % of the growth of the VLP abundance (p=0,013). In the winter season, connections between VLP and other biological variables were not found. As a conclusion, in the growing season algae cells (Inc. cyanobacteria) are dominant hosts for viruses. Dominant host probably varies between the seasons. Between littoral ja pelagic zones, differences of abundance of VLP, bacteria and algae biomass were not found. This was probably caused by windy conditions creating similar conditions between zones. There is a high abundance of viruses in productive layer in Lake Vesijärvi year-round. Viruses have direct and indirect interactions with algae and bacteria varying in different time scales. It is likely that viruses have interactions also with other functional groups of the lake microbial network. The results of this study confirmed, for the first time in Finland, the virus abundance, its variation and interactions with functional groups of microbial network. The role of viruses in biochemical cycles of fresh water ecosystems need to study more in Finland.