1. Endorheic soda pans are among the highest dissolved organic carbon (DOC) content aquatic systems on the planet with concentrations up to 1 g/L. Considering the importance of inland waters in the global carbon cycle, understanding the drivers of such outstanding organic carbon pools is eminent. The soda pans of the Carpathian Basin present a wide variability of biotic and abiotic characteristics that provide an adequate system to assess the determinants of extreme high DOC concentrations. Here, we demonstrate through a multi-site comparison, a multi-year seasonal monitoring, and a laboratory experiment that the dissolved organic matter content of the highest DOC concentration soda pans is primarily of groundwater and emergent macrophyte origin. 2. More precisely, the multi-site comparison of 14 soda pans revealed that variation of coloured dissolved organic matter (CDOM) content of the surface water of soda pans is partially explained by the CDOM content (22% of variation) of local groundwater, indicating the significant role of allochthonous terrestrial DOC sources. Further 23% of CDOM variation could be accounted for by Bolboschoenus maritimus species-specific emergent macrophyte cover, while the contribution of Phragmites australis cover was only minor. 3. In line with the results of the multi-site comparison, our decomposition experiment demonstrated that both B. maritimus and P. australis have the potential to release substantial amount of organic matter into soda pans. However, the organic matter release of B. maritimus leads to twice as high DOC and 3.5-times higher CDOM concentrations than P. australis. Considering previous organic matter release studies, we concluded that P. australis is a relatively low organic matter releaser emergent macrophyte, and therefore the species composition of emergent macrophytes has to be carefully considered in autochthonous plant-derived DOM estimations. 4. Finally, the multi-year seasonal monitoring of two distinctive soda pans showed that the high organic matter concentrations depend not only on their intrinsic characteristics but also on interannual variability. More precisely, we demonstrated that the highest CDOM and DOC concentrations that occurred in a coloured (i.e. brown, low total suspended solids) soda pan with extensive (95%) macrophyte cover dominated by B. maritimus were measured in a period characterised by high This is an open access article under the terms of the Creat ive Commo ns Attri bution License, which permits use, distribution and reproduction in any medium, provided the original work is properly cited.

Little is known about how various substances from living and decomposing aquatic macrophytes affect the horizontal patterns of planktonic bacterial communities. Study sites were located within Lake Kolon, which is a freshwater marsh and can be characterised by open-water sites and small ponds with different macrovegetation (Phragmites australis, Nymphea alba and Utricularia vulgaris). Our aim was to reveal the impact of these macrophytes on the composition of the planktonic microbial communities using comparative analysis of environmental parameters, microscopy and pyrosequencing data. Bacterial 16S rRNA gene sequences were dominated by members of phyla Proteobacteria (36%-72%), Bacteroidetes (12%-33%) and Actinobacteria (5%-26%), but in the anoxic sample the ratio of Chlorobi (54%) was also remarkable. In the phytoplankton community, Cryptomonas sp., Dinobryon divergens, Euglena acus and chrysoflagellates had the highest proportion. Despite the similarities in most of the measured environmental parameters, the inner ponds had different bacterial and algal communities, suggesting that the presence and quality of macrophytes directly and indirectly controlled the composition of microbial plankton.

Increasing human impact on the environment is causing drastic changes in disturbance regimes and how they prevail over time. Of increasing relevance is to further our understanding on biological responses to pulse disturbances (short duration) and how they interact with other ongoing press disturbances (constantly present). Because the temporal and spatial contexts of single experiments often limit our ability to generalize results across space and time, we conducted a modularized mesocosm experiment replicated in space (5 lakes along a latitudinal gradient in Scandinavia) and time (2 seasons, spring and summer) to generate general predictions on how the functioning and composition of multi-trophic plankton communities (zoo-, phyto-and bacterioplankton) respond to pulse disturbances acting either in isolation or combined with press disturbances. As pulse disturbance, we used short-term changes in fish presence and as press disturbance, we addressed the ongoing reduction in light availability caused by increased cloudiness and lake browning in many boreal and subarctic lakes. First, our results show that the top-down, pulse disturbance had the strongest effects on both functioning and composition of the three trophic levels across sites and seasons, with signs for interactive impacts with the bottom-up, press disturbance on phytoplankton communities. Second, community composition responses to disturbances were highly divergent between lakes and seasons: temporal accumulated community turnover of the same trophic level either increased (destabilization) or decreased (stabilization) in response to the disturbances compared to control conditions. Third, we found functional recovery from the pulse disturbances to be frequent at the end of most experiments. In a broader context, these results demonstrate that top down, pulse disturbances, either alone or with additional constant stress upon primary producers caused by bottom-up disturbances, can induce profound but often functionally reversible changes across multiple trophic levels, which are strongly linked to spatial and temporal context dependencies. Furthermore, the identified dichotomy of disturbance effects on the turnover in community composition demonstrates the potential of disturbances to either stabilize or destabilize biodiversity patterns over time across a wide range of environmental conditions.

Beside sodium chloride, inland saline aquatic systems often contain other anions than chloride such as hydrogen carbonate and sulfate. Our understanding of the biological effects of salt composition diversity is limited; therefore, the aim of this study was to examine the effect of different anions on the growth of halophilic bacteria. Accordingly, the salt composition and concentration preference of 172 strains isolated from saline and soda lakes that differed in ionic composition was tested using media containing either carbonate, chloride or sulfate as anion in concentration values ranging from 0 to 0.40 mol/L. Differences in salt-type preference among bacterial strains were observed in relationship to the salt composition of the natural habitat they were isolated from indicating specific salt-type adaptation. Sodium carbonate represented the strongest selective force, while majority of strains was well-adapted to growth even at high concentrations of sodium sulfate. Salt preference was to some extent associated with taxonomy, although variations even within the same bacterial species were also identified. Our results suggest that the extent of the effect of dissolved salts in saline lakes is not limited to their concentration but the type of anion also substantially impacts the growth and survival of individual microorganisms.

Results of a comparative investigation on five Cernosvitoviella species from Hungarian Sphagnum mires including their distribution and the description of a new species, Cernosvitoviella farkasi sp. n., are presented in this paper. Cernosvitoviella atrata, C. aggtelekiensis, C. crassoductus and C. farkasi sp. n. could be easily distinguished from each other based on both morphological and molecular taxonomic analyses. However, C. minor seems to be a species complex on the basis of these investigations, so it was referred as C. minor sensu lato. The status of the C. minor variants requires further studies.

1.Endorheic soda pans are among the aquatic systems that have the highest dissolved organic carbon (DOC) content on the planet with concentrations reaching values close to 1 g L−1. Considering the importance of inland waters in the global carbon cycle, the understanding of the drivers of such outstanding aquatic organic carbon pools is eminent. The soda pans of the Carpathian Basin present a wide variability of biotic and abiotic characteristics that provides an adequate system to assess the determinants of the extreme high DOC concentrations of soda pans. Here we demonstrate through a multisite comparison, a multiyear seasonal monitoring, and a laboratory experiment that the dissolved organic matter content of the highest DOC concentration soda pans is primarily of groundwater and emergent macrophyte origin.2.More precisely, the multisite comparison of 14 soda pans revealed that the variation of colored dissolved organic matter (CDOM) content of the pans is partially explained by the CDOM content (21% of variation) and conductivity (14%) of the local groundwater indicating significant role of allochthonous terrestrial DOC sources. However, 46% of the variation in CDOM content of the studied soda pans could be accounted for the dominant type of emergent macrophyte with Bolboshoenus maritimus dominated macrophyte cover leading to higher CDOM content than Phragmites australis. 3.In line with the results of the multisite comparison, we demonstrated by a decomposition experiment that both B. maritimus and P. australis have the potential to release substantial amount of organic matter into soda pans. However, the organic matter release of B. maritimus is much more intensive than that of P. australis leading to twice as high DOC and 3.5-times higher CDOM concentrations. In general, considering previous organic matter release studies we concluded that P. australis is a relatively low organic matter releaser emergent macrophyte, and therefore the species composition of emergent macrophytes has to be considered in autochthonous plant-derived DOM estimations.4.Finally, the multi-year seasonal monitoring of two distinctive soda pans showed that the high organic matter concentrations of the pans depends not only on their intrinsic characteristics but also on interannual variability. More precisely, we demonstrated that the highest CDOM and DOC concentrations occurred in a colored (i.e., brown, low TSS) soda pan that had extensive (95%) macrophyte cover dominated by B. maritimus in a period characterized by high pH due to low water levels, which were presumably the consequence of increased evaporation due to decreased precipitation and above average temperature. Considering the trends of climate change in Central-Europe (i.e., increased temperature and modified precipitation regimes), our results indicate that extremely high organic matter concentrations in soda pans might become more frequent in the near future.

Lakes located in the boreal region are generally supersaturated with carbon dioxide (CO2), which emerges from inflowing inorganic carbon from the surrounding watershed and from mineralization of allochthonous organic carbon. While these CO2 sources gained a lot of attention, processes that reduce the amount of CO2 have been less studied. We therefore examined the CO2 reduction capacity during times of phytoplankton blooms. We investigated partial pressure of CO2 (pCO2) at times of blooms dominated by cyanobacteria (lake Erken, Sweden) or dominated by the nuisance alga Gonyostomum semen (lake Erssjön, Sweden) during two years. Our results showed that pCO2 and phytoplankton densities remained unrelated in the two lakes even during blooms. We suggest that physical factors, such as wind-induced water column mixing and import of inorganic carbon via inflowing waters suppressed the phytoplankton signal on pCO2. These results advance our understanding of carbon cycling in lakes and highlight the importance of detailed lake studies for more precise estimates of local, regional and global carbon budgets.

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