ИСТИНА

Hypolithic biocrust (occurs beneath rock debris, stone pavements) is often not perceived as a soil horizon and an integral part of the whole bio-abiotic profile. However, the profiles with cryptogamic hypolithic horizons could act as precursors to the more advanced soil formations or even the steady state soil bodies if occur in regions with climatic extremes. Hypolithic horizons dominated by cyanobacteria are the substantial spots for primary production and nitrogen source in oligotrophic landscapes of East Antarctica giving the rise to the more advanced biotic components (if conditions are favorable). Organo-mineral interactions that take place in hypolithic layers significantly alter the mineral matrix with some byproducts being vertically and laterally redistributed in soil. Understanding soils with cryptogamic hypolithic horizons is of fundamental importance, since they are possibly among the closest modern analogues of protosoils that existed before the higher vascular plants with root systems established. As in many other parts of Antarctica a significant portion of organic matter in the Larsemann Hills oasis (69°24’S, 76°14’E) is produced by hypoliths in cryptic niches underneath the stone pavements on loose sediments and by endoliths inside the fissure network of hard rocks. The survey conducted in Larsemann Hills revealed that hypolithic bio-abiotic systems (soils) together with the endolithic ones (soloids) occupy from 20 to 60% of the wet valleys floors and slopes area. The spatial distribution of various types of hypolithic biocrusts (cyanobacteria, green algae, fungi and bryophyte dominated series), its thickness, moisture content, carbon and nitrogen content/stocks, as well as C/N ratios were studied at a detailed scale at several key sites along the grid of 10x10 m with a step of 1 m (121 sampling points each). The data received are evident that microbial and cryptogamic photoautotrophs activity in hidden habitats under the stone pavements could lead to the substantial organic matter accumulation in extreme environment of East Antarctica - up to 5% of C and 0.4% of N. C/N ratios in modern hypolithic biocrust varied between 7 to 30 and δ13C between -24 to -30‰, both indicating differences in microbial and cryptogamic photoautotrophs contribution. Carbon dioxide emission (g C-CO2/m2 per hour) altered between 0.008 from the surface of cyanobacteria dominated hypolithic biocrust to 0.023 from the bryophyte dominated one. The long-term preservation of organic matter in hypolithic environment is questionable in a number of locations in the Larsemann Hills since the values of fraction modern (F14C) according to the radiocarbon data surpass “1” in some cases. This contrasts with 14C “ages” for endolithic systems on surrounding slopes of the valley exceeding 500 and sometimes 1000 yr BP. However, once organogenous material of hypolithic origin is buried under sand and gravel only 2-5 cm deeper than its common location it could persist for long periods with 14C estimates up to 1100 yr BP. As evidenced by optical and scanning electron microscopy this old organogenous material of hypolithic origin still retains clear filamentous structure of cyanobacteria biofilm as well as remnants of EPS stabilized mainly by amorphous Al-Si compounds. Both “fresh” hypolithic organic carbon pool utilized by biogenic and abiogenic processes (e.g. erosion) and the older one, which is more stabilized through burial, are superimposed on the really old carbon pool with 14C “ages” exceeding 6000 yr BP. The latter starts from the depth of 8-10 cm and has a complex origin comprising relocated endolithic microfossils, lacustrine organic matter and carbon from other sources. It resembles the dual carbon pool model of a common soil with faster pool in topsoil and slower one in subsoil.