Natural spatial subsidies in continental Antarctic soil

The soils of the McMurdo Dry Valleys are hypothesized to rely on external sources of nutrients (carbon, nitrogen, etc). The importance of these spatial subsidies on productivity and biological diversity of dry valley soils was investigated over several seasons in the Garwood Valley. Sampling of the soil, microbial mats and foam from each identified landform and from Lake Colleen was undertaken for analysis of a variety of soil biological and chemical properties in order to gain an idea of the general spatial variation of these properties (before experimental work) and to determine the size of the soil microbial communities, the rates of microbial respiration and the abundance of selected invertebrate groups. Soil samples were collected and analysed to quantify carbon and nitrogen pools, potential decomposition and nitrogen release under optimal conditions and potential microbial use of a variety of test C and N substrates. The importance of spatial subsidy materials on the four different landforms was tested with the addition of lakeshore foam and algal mats at two levels of application, plus appropriate treatment controls. Pre-treatment soil samples were taken for a variety of chemical analysis to establish baseline parameters. After subsidy applications, field measurements were made of the short -term changes (over the first six days after treatment application) in in-situ microbial activity and the composition of gases being released into the atmosphere. After six days, a second set of soil samples were collected for post treatment measurements of soil community composition and diversity, potential microbial activity and decomposer processes. Soil samples were again taken 2 years later for medium term respiratory processes but also for laboratory controlled replicate experiment for in-situ confirmation of initial nitrogen limitation and later carbon limitation. Studies were in the 01/02, 02/03 and 04/05 seasons in the Garwood Valley.