Resource Limitations to Soil Microbial Activity In An Antarctic Dry Valley.

Although Antarctic dry valley soils function under some of the harshest environmental conditions on the planet, there is significant biological activity concentrated in small areas in the landscape. These productive areas serve as a source of C and N in organic matter redistributed to the surrounding biologically impoverished soils. We conducted a three year replicated field experiment involving soil amendment with C and N in simple (glucose and NH₄Cl) and complex (glycine and lacustrine detritus) forms to evaluate the resource limitation of the soil microbial community in an Antarctic dry valley. The respiratory response for all substrates was slow, with a significant but weak response to NH₄Cl, followed by a more widespread response to all substrates after two years and in laboratory incubations conducted three years after substrate addition. This response suggests that the soil microbial community is N-limited, and when that constraint is alleviated, the organisms are able to access a pool of stored C that they could not metabolise before.  The effects of added C and N substrates on respiration rate under laboratory conditions were more rapid and significant than the response rates measured in situ. Since the spatial constraints that had probably limited access to soil resources by microorganisms in the field would have been removed in the laboratory incubation this finding highlights the severe spatial constraints on access to resources in these soils.