Isotopic evidence for the provenance and turnover of organic carbon by soil microorganisms in the Antarctic dry valleys

摘要

The extremely cold and arid dry valleys in the Southern Victoria Land region of Antarctica are one of the most environmentally harsh terrestrial ecosystems supporting organisms. The dry valleys are characterized by a combination of low temperatures and lack of liquid water that severely limit the abundance and activity of terrestrial organisms. Nevertheless, the soils contain organic C and N, a relatively large proportion of which is inorganic N, emit CO_2 produced by heterotrophic respiration and support active communities of heterotrophic soil organisms. The biogeochemical transformations of carbon and other nutrients in the dry valleys soils are exclusively driven by microorganisms. The dry valleys lack vascular plants and the cryptogamic vegetation is both sparse and inconspicuous. In situ primary production by mosses, lichens, terrestrial cyanobacteria and algae, including production in cryptic microbial communities that grow endolithically (literally growing in the interstitial spaces in fissured rock, where there may be more liquid water and where they are protected from the radiation and the abrasive and drying effects of the wind), is very limited. However, there are several other potential sources of organic C and N to support terrestrial heterotrophs, including redistributed detritus from modern lacustrine cyanobacteria, marine detritus, and the remnants of ancient organic deposits from palaeo-lakes, which is also believed to be of algal and cyanobacterial origin. The natural abundanceof ~(13)C and ~(15)N in source organic materials and soils have been examined to obtain evidence for the provenance of the soil organic matter. The organic matter in soils remote from sources of liquid water or where lacustrine productivity was low hadisotope signatures characteristic of endolithic (lichen) sources, whereas at more sheltered and productive sites, the organic matter in the soils that was a mixture mainly lacustrine detritus and moss-derived organic matter.