Nutrient and Thermal Regime, Microbial Biomass, and Vegetation of Antarctic Soils in the Windmill Islands Region of East Antarctica (Wilkes Land)

Abstract

In the antarctic summer of 1996, permafrost-affected cold soils close to the Australian Casey Station in the Windmill Islands region (Wilkes Land) were investigated to determine in what way the thermal and nutrient regimes in the antarctic soils are related to microbial biomass and vegetation patterns. The soils are characterized by a high content of coarse mineral particles and total organic carbon (TOC) and a low C/N ratio (mean 11). Despite the low pH values (mean 4.0) the soils are rich in nutrients due to an input from seabirds (existing or abandoned nesting sites) and an eolian distribution of fine-grained soil material in the landscape. Vegetation influences TOC storage and the cation exchange capacity in the uppermost soil horizons, whereas total N and most nutrient levels are not affected by the vegetation, but by seabird droppings. The present nutrient level does not affect plant adaptation, because the K, Mg, and P contents are often extraordinarily high. This suggests that nutrient supply is not a limiting factor, whereas microclimate effects, such as moisture availability and ground-level wind speed, have a primary influence on plant growth. Soil-surface temperature measurements indicate a strong variability in microclimate due to small-scale variations in geomorphological surface features. Bacteria are found in all soil horizons, but not algae and yeast. Soil microbial counts are weakly correlated to the C/N ratios and soil surface temperatures. High TOC and clay contents probably improve the soil water-holding capacity and TOC contributes to the microbial food supply. The investigated microbial parameters are weakly correlated to the present vegetation carpet, the lowest counts are found in the soils with scattered or no vegetation cover.