Ice Free Regions

Natural spatial subsidies in continental Antarctic soils

Principal Investigator: Ashley Sparrow
Organisation: University of Canterbury

What we do: We conduct soil surveys and experiments in Victoria Land’s dry valleys where lake-derived resources (microbial mats and water-surface foams derived from algae and cyanobacteria) enter the soil foodweb by aerial redistribution. We quantify the spatial variability amongst the landscape units in these valleys in terms of microbial composition and functioning of the soil system, and the level of resource inputs. In an experiment, we directly apply microbial mat and foam collected from the lakeshore, and contrast their effects on the soil system with treatments of simpler substrates (e.g. carbon as glucose and nitrogen as ammonium chloride). We measure how the soil system develops after substrate addition, including community composition and diversity, microbial activity, and key decomposer processes including carbon and nitrogen release patterns. These experiments are framed as tests of a new model of landscape function in the dry valleys.

Why we do it: Organisms in Antarctic dry valley plant-soil systems are very stressed and, because of low intensity of indigenous productivity, rely to some extent on resources transported from external sources by wind or water (spatial subsidies). The magnitude and effects of such subsidies on these ecosystems are largely unexplored, but are likely to significantly influence community structure, ecosystem function and responsiveness to environmental change.

What we have found so far: Amounts of carbon and nitrogen in dry valley soils, and their indigenous productivity, vary by 100-fold between landscape units and all three factors are strongly positively correlated with availability of liquid water in the soil during the summer season; this finding is consistent with patterns in the hot deserts of the world.  Within any landscape unit, the soil carbon pool decreases with distance from lakes, consistent with the hypothesis that lakes are significant sources of wind-blown algal and cyanobacterial materials.  Soil biota respond rapidly to experimental additions of algae and cyanobacteria when soil is warm (e.g. 5°C) and moist.  Biota respond strongly to more controlled additions of both glucose and ammonium chloride, suggesting that soil biota may be variously limited by carbon or nitrogen; the time traces of these responses suggest that there may be switching from carbon limitation to nitrogen limitation, and vice versa, under changing environmental conditions.  There is evidence for anaerobic and methanogenic bacteria from gas samples collected from different depths in soil profiles; these bacteria are patchily located in soils and varying in activity through time, indicating large below-ground heterogeneity of biological activity.

Recent Publications
Hopkins, D.W et. al. 2005.  Soil micro-organisms in Antarctic dry valleys: resource supply and utilization.  in: G.M. Gadd, K.T. Semple & H.M. Lappin-Scott (eds).  SGM Symposium 65: Micro-organisms and Earth Systems – Advances in Geomicrobiology.  Cambridge University Press, Cambridge.  pp.71-84.