Friday, August 7, 2009

PS 78-29: Spatial variation in organic matter and soil biota in the McMurdo Dry Valleys, Antarctica

J. E. Barrett1, David W. Hopkins2, Ian D. Hogg3, and S. Craig Cary3. (1) Virginia Tech, (2) University of Stirling, (3) University of Waikato


The Antarctic Dry Valleys are among the most extreme soil environments on earth.  In 1903 R.F. Scott described an apparent lack of life in the dry valleys, yet recent evidence reveals microbial diversity comparable to hot deserts.  While Scott’s impression has persisted into modern times, an emerging view of the dry valleys suggests a greater potential for biological influence over ecosystem functioning than previously recognized.  We present data collected in 2008/2009 by the New Zealand-International Polar Year Terrestrial Antarctic Biological Survey.  The goal of this project is to elucidate the factors controlling assembly of soil communities from their most simple manifestation as strictly prokaryotic assemblages to the richest and most productive ecosystems consisting of linked microbial-metazoan trophic groups.  Understanding controls over distribution of organisms, assembly of biotic communities and ecological processes is essential to developing hypotheses and prediction about the influence of climate change and other human impacts on this unique environment.  This project uses an interdisciplinary approach to link the underlying physical properties of local soils, including lithology, geomorphology, soil chemistry and microclimate with the distribution of biota in a landscape model that will scale to the region.  Since availability of organic matter is hypothesized to be a major limitation to the assembly of active, multi-trophic communities, understanding the spatial variation in source pools of organic matter is essential to the broader goals of elucidating dry valley biocomplexity.   


Stable isotopic composition suggests that multiple pools of organic matter contribute to soil carbon and nitrogen in these environments, including cyanobacterial mats (-20 to -5 δ 13C ‰) and moss associated with adjacent aquatic environments (-25 to -27 δ 13C ‰), and lichens and lithic communities in the dry mineral soils (-25 to -30 δ 13C ‰).  Microbial biomass and invertebrate abundance are strongly correlated with organic matter.  Relationships among the density and composition of these cryptogam communities with below-ground microbial and metazoan assemblages suggest that soil diversity may be broadly predictable by the distribution of organic matter content and composition.  The relative importance of these sources to regional stocks of carbon and food webs will be discussed.