Salinity-induced succession of phototrophic communities in a southwestern Siberian soda lake during the solar activity cycle

Abstract

A variety of lakes located in the dry steppe area of southwestern Siberia are exposed to rapid climatic changes, including intra-century cycles with alternating dry and wet phases driven by solar activity. As a result, the salt lakes of that region experience significant fluctuations in water level and salinity, which have an essential impact on the indigenous microbial communities. But there are few microbiological studies that have analyzed this impact, despite its importance for understanding the functioning of regional water ecosystems. This work is a retrospective study aimed at analyzing how solar activity-related changes in hydrological regime affect phototrophic microbial communities using the example of the shallow soda lake Tanatar VI, located in the Kulunda steppe (Altai Region, Russia, southwestern Siberia). The main approach used in this study was the comparison of hydrochemical and microscopic data obtained during annual field work with satellite and solar activity data for the 12-year observation period (2011-2022). The occurrence of 33 morphotypes of cyanobacteria, two key morphotypes of chlorophytes, and four morphotypes of anoxygenic phototrophic bacteria was analyzed due to their easily recognizable morphology. During the study period, the lake surface changed threefold and the salinity changed by more than an order of magnitude, which strongly correlated with the phases of the solar activity cycles. The periods of high (2011-2014; 100-250 g/L), medium (2015-2016; 60 g/L), extremely low (2017-2020; 13-16 g/L), and low (2021-2022; 23-34 g/L) salinity with unique biodiversity of phototrophic communities were distinguished. This study shows that solar activity cycles determine the dynamics of the total salinity of a southwestern Siberian soda lake, which in turn determines the communities and microorganisms that will occur in the lake, ultimately leading to cyclical changes in alternative states of the ecosystem (dynamic stability).

Keywords: Diversity; Dynamic stability; Phototrophs; Salinity; Soda lakes; Solar activity.

Graphical abstract

Fig. 1

Geographical location and the general view of the soda lake Tanatar VI: (a) approximate territories of southwestern (SW) and southeastern (SE) Siberia in the map of Eurasia; (b) Tanatar group of lakes (the grey line indicates the asphalt road); (c–d) general view of the sampling site in 2014 (c), 2018 (d), and 2022 (e). The red asterisk indicates the sampling site; the red arrow points to the same point in different years. (For interpretation of the references to color in this figure legend, the reader is referred to the Web version of this article.)

Fig. 2

Soda lakes Tanatar VI and Tanatar V in summer periods during 2011–2022. NDWI – normalized difference water index, NDVI – normalized difference vegetation index, False color – composite satellite image in near infrared, red and green bands. See Table S1 for more details on each image, and for a thorough explanation of the implications of the color scale, see Section 2.4. (For interpretation of the references to color in this figure legend, the reader is referred to the Web version of this article.)

Fig. 3

Sunspot number progression and changes in surface area of the soda lake Tanatar VI for the study period 2011–2022. Smoothed monthly values are a 13-month weighted, smoothed version of the monthly averaged data.

Fig. 4

Change in total salinity, surface area and microbial communities of the soda lake Tanatar VI during the summer periods from 2011 to 2022. * – cases of precipitation of carbonate minerals at the bottom of the lake in 2021–2022; n/d – no data.

Fig. 5

Morphotypes of key phototrophs identified in the soda lake Tanatar VI (Kulunda steppe) during 2011–2022 study period. Eukaryotic algae: 1. Picocystis salinarum, 2. Ctenocladus circinnatus; Cyanobacteria: 3. Anabaenopsis issatchenkoi, 4. Anabaenopsis nadsonii, 5. Calothrix cf. elenkinii, 6. Nodularia harveyana, 7. Nodularia cf. sphaerocarpa, 8. Nostoc cf. paludosum, 9. Nostoc cf. punctiforme, 10. cf. Trichormus variabilis, 11. cf. Trichormus sp., 12. Sodalinema sp., 13. Nodosilinea sp., 14. cf. Halomicronema sp., 15. Phormidium cf. etoshii, 16. Spirulina major, 17. Leptolyngbya tenuis, 18. Leptolyngbya cf. foveolarum, 19. Leptolyngbya sp., 20. Pseudanabaena sp., 21. Oscillatoria cf. tenuis, 22. Arthrospira maxima, 23. Limnospira fusiformis, 24. Leibleinia sp.1, 25. Leibleinia sp.2, 26. cf. Jaaginema pseudogeminatum, 27. Chroococcus turgidus, 28. cf. Chroococcus distans, 29. cf. Synechocystis salina, 30. cf. Synechocystis minuscula, 31. cf. Cyanobacterium stanieri, 32. cf. Merismopedia warmingiana, 33. cf. Aphanocapsa salina, 34. cf. Geminocystis sp., 35. Euhalothece sp.; Anoxygenic phototrophic bacteria: 36. colonies of Ectothiorhodospira sp., 37. Chromatium sp., 38. Thiocapsa sp., 39. “Cand. Viridilinea mediisalina”. The letter "A" next to the number indicates the akinetes of the morphotype indicated by this number, and the letter “H” indicates heterocysts. All images are at the same scale. Scale bar – 10 μm.

Fig. 6

The total salinity range recorded in the soda lake Tanatar VI during the study period from 2011 to 2022 (grey line), and the salinity ranges in which various cyanobacteria and other key phototrophs were detected. Solid lines – detection in brine (and in SBFs if available), dashed lines – detection only in SBFs (but absent in brine at these salinities). Violet lines – algae, green lines – filamentous non-heterocystous cyanobacteria, blue lines – unicellular cyanobacteria, orange lines – heterocystous cyanobacteria, red lines – anoxygenic phototrophic bacteria. (For interpretation of the references to color in this figure legend, the reader is referred to the Web version of this article.)

Fig. 7

Clustering of phototrophic complexes in brine (A) and SBFs (B) based on the presence/absence matrices (Tables S4 and S5) of the key phototrophic morphotypes. NM – total Number of Morphotypes found in samples.