| The McMurdo Dry Valleys of Antarctica are one of the most extreme terrestrial environments on Earth. The polar desert soils of this ecosystem experience cold temperatures and are often saline and desiccated, yet they contain low-diversity communities of invertebrates (primarily nematodes). Nematodes in soils are capable of employing an inactive, anhydrobiotic survival strategy in response to adverse conditions. The objective of this dissertation was to study the role of anhydrobiosis in the ecology of dry valley soil nematodes. First, I studied nematode anhydrobiosis with respect to soil moisture, salinity, and temperature over seasonal and diurnal temporal scales. For these experiments, I developed a sampling method to fix the status of nematodes in samples. Nematodes communities were often found with high proportions (>60%) in anhydrobiosis. More nematodes were anhydrobiotic in drier soils. Nematode anhydrobiosis did not vary greatly over temporal scales, but addition of moisture to soils was a strong trigger for emergence from anhydrobiosis. Second, I studied nematode communities collected across a stream channel. I predicted that the transfer of moisture and salts between soils and stream sediments would correlate to the structure of invertebrate communities. Diversity, but not abundance, of invertebrates was correlated to moisture in these samples. Assemblages of nematodes, rotifers, and tardigrades were found in the wettest samples, with the highest productivity. In contrast, in the driest soils studied, communities consisted almost entirely of a single nematode species, Scottnema lindsayae. Finally, I studied nematode activity in conjunction with field and microcosm studies of decomposition, a process regulated by soil biota. In microcosms, decomposition of cotton strips, soil microbial respiration, and nitrification were all accelerated by the addition of water over a nine-month incubation at 10°C. In the field, decomposition of cotton strips was negligible after two years in soils, even when nematode activity was stimulated. The results of these experiments suggest that the activity of soil biota and the functions they perform are limited in the dry valleys. Understanding where and when soil nematodes in the dry valleys are anhydrobiotic and inactive is important to determining how the extreme environment influences biological processes, such as decomposition. |
