Isotope Composition of Carbon and Nitrogen in Subterranean Karst Geosystems Components: The Case of Excursion Caves of Cis-Urals and the Caucasus

The results of the isotopic composition studies (δ13С / δ15N) of phototrophic communities in the karst caves are presented. The caves were rangier by different physical-geographical regions: mountain taiga (Kungurskaya Ledyanaya cave) and mountain humid-subtropical forest (Akhshtyrskaya or Bolshaya Kazchebrodskaya cave and Novoafonskaya cave named after G.Sh. Smyr). The fractionation of carbon and nitrogen stable isotopes were studied in the communities of phototrophic organisms of subterranean landscapes (lampenflora), as well as the influencing of one’s to the soil-like bodies (soloids) under these communities. That is discussed the difference of lampenflora phytomass isotopic composition in compare with terrestrial similar systematic and ecological groups of phototrophs towards enrichment with isotopes 12C and 14N. An increase of interests of light carbon and nitrogen isotopes was also noted for cave soloids in comparison with soils on the day surface. The ratio of carbon stable isotopes varies from –47.3 to –32.4‰ for subterranean ecosystems and from –35.5 to –26.8‰ for control samples (daylight surface). The isotopic composition of nitrogen shows a smaller variation from –8 to –1.8‰—in underground habitats, and from –3.5 to +2.0‰—on the surface. The hypothesis regarding the specifics of gas exchange in subterranean space and biological circulation of carbon dioxide in a semi-closed atmosphere was created. This hypothesis is confirmed by the trend of accumulation of the 12C isotope in lampenflora and soloids with distance from the cave entrance, which is due to the reduction of air circulation. The data of carbon and nitrogen isotope composition for the lampenflora and soloids from karst caves in the different physico-geographical zone are also generalized and systematized in this work, there is a geographical trend, but it is necessary to increase the number of studied objects from different natural zones to confirm this conclusion.

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