Effects of summer desiccation on desmid microflora of ombrogenous pools in central-European mountain peat bogs

Seasonal desiccation of ombrogenous pools caused by high summer temperatures and changing precipitation patterns is a consequence of ongoing climate change in central-European peat bogs. This phenomenon may be a critical stress factor for the microphytobenthos that thrive in these shallow aquatic habitats. One of the abundant groups in the phytobenthos of ombrogenous bog pools are desmids, a lineage of streptophyte algae closely related to vascular plants. In this study, we tested whether the assemblages of these microalgae are affected by differential desiccation of pools in three mountain bogs in the Ore Mountains (Czech Republic). In addition to the dynamics of species composition, the study focused on analysing the desmid-based NCV (nature conservation value) index to assess the conservation value of individual sites. The gradient of studied pools ranged from those found to be dried out in all field surveys during the summer to those constantly flooded. The varying desiccation rate of pools was closely related to their depth. The shallower pools with higher desiccation rates had slightly lower pH and higher concentrations of dissolved organic carbon, total nitrogen and Pb. However, virtually all pools were highly acidic, with a pH below 4.0. The most frequently detected species were Actinotaenium silvae-nigrae and Staurastrum margaritaceum, which occurred at most sites. Conversely, the more sensitive taxa, such as Cosmarium pygmaeum, C. sphagnicolum or S. scabrum, which have high indication values for the calculation of the NCV index, were also found in several pools. The desiccation rate was significantly related to the species composition. In addition, the NCV index values of pools with higher desiccation rates were lower compared to pools with a more stable hydrological regime. In particular, Tetmemorus laevis, S. hirsutum, and S. furcatum var. aciculiferum were more likely to occur at sites that did not dry out completely during the summer season. These species can therefore be considered as indicators of bogs with relatively low rates of seasonal desiccation. Conversely, Cosmarium obliquum was the only species that preferred pools with a longer desiccation period. The study showed that hydrological fluctuation represents a key environmental factor for desmid phytobenthos in ombrogenous bog pools. As the frequency of extreme climate fluctuations increases, desiccation events in central-European bogs are likely to occur more frequently and last longer. The study has shown that this environmental disturbance is likely to lead to significant shifts in the peat bog microflora.