Controls on the distribution of productivity and organic resources in Antarctic Dry Valley soils

Abstract

The Antarctic Dry Valleys are regarded as one of the harshest terrestrial habitats on Earth because of the extremely cold and dry conditions. Despite the extreme environment and scarcity of conspicuous primary producers, the soils contain organic carbon and heterotrophic micro-organisms and invertebrates. Potential sources of organic compounds to sustain soil organisms include in situ primary production by micro-organisms and mosses, spatial subsidies from lacustrine and marine-derived detritus, and temporal subsidies ('legacies') from ancient lake deposits. The contributions from these sources at different sites are likely to be influenced by local environmental conditions, especially soil moisture content, position in the landscape in relation to lake level oscillations and legacies from previous geomorphic processes. Here we review the abiotic factors that influence biological activity in Dry Valley soils and present a conceptual model that summarizes mechanisms leading to organic resources therein.

Figure 1

Generalized relations of ice and liquid water distribution, net water fluxes, prevailing winds and primary producers with geomorphology in continental Antarctica. The diagram has been adapted from Janetschek (1970). It should be noted that the water fluxes are indicative net fluxes, and it is not intended to imply that precipitation only occurs during the winter and that evaporation only occurs during the summer in the Dry Valleys.

Figure 2

Summary of soil moisture and water fluxes for soils under different environmental conditions in the Dry Valleys. For justification of the 2–5% cut-off in water content see Treonis et al. (1999), Elberling (2003), Barrett et al. (2004) and Elberling et al. (in press).

Figure 3

Examples of sources of organic resources for heterotrophic organisms in the Dry Valleys: (a) surficial lichen; (b) hypolithic algal/cyanobacterial community (the stone was buried to the depth indicated by the arrow); (c) endolithic community in sandstone (the arrow indicates organisms (black coloration) exposed by exfoliation of the sandstone); (d) hypolithic moss; (e) surficial moss in ephemeral stream bed; (f) remains of Adélie penguin; (g) mummified crab-eater seal; (h) area of lake shore from which cyanobacterial mat has been removed (presumably by wind); (i) wind-blown foam (presumed to be derived from decomposing lacustrine detritus) accumulation at lake shore; (j) lacustrine detritus stranded close to lake shore following a recent fall in lake level; (k) cyanobacterial mat from ancient lake shore exposed following erosion of the overlying soil/sediment.

Figure 4

Conceptual summary of the sources and transfers of organic resources in the Antarctic Dry Valleys.