Long-term experimental warming reduces soil nematode populations in the McMurdo Dry Valleys, Antarctica

Abstract

Climate models predict significant future warming in polar regions. In the McMurdo Dry Valleys, Antarctica, projected summer climate warming is expected to increase snow and glacial melt, resulting in higher stream discharge, rising lake levels, and an increase in areas of moist soil, but the potential influence of warming and associated changes in hydrology on the soil ecosystem is poorly understood. To examine the effects of soil warming and changes in the availability of liquid water on populations of soil invertebrates and their habitat, we established a full-factorial warming and water addition experiment at one experimental site in each of the three hydrologic basins of Taylor Valley, Antarctica, and measured responses over 8 years. We hypothesized that an increase in temperature and moisture together would enhance habitat suitability for soil invertebrates thereby increasing abundance, biomass and diversity of the soil animal communities. Instead, warming treatments had an overall negative effect on density and body size of the microbial-feeding nematode Scottnema lindsayae, the dominant animal in the dry valleys, which decreased by 42% in warmed plots. While experimental moisture additions as a single annual pulse had no effect on nematodes, the surface flooding of one site from rapid melting of upslope subsurface ice (the result of an unusual natural warming event) drastically altered soil moisture, salinity, and animal communities; mortality of S. lindsayae increased and densities decreased. This extreme soil wetting event also resulted in an increase in chlorophyll a and populations of Eudorylaimus spp, a nematode species that prefers moist to wet habitats and feeds on soil micro-algae. Our results suggest that warming in the dry valleys could significantly affect soil nematode populations and species composition both directly and indirectly by altering species-specific habitat suitability for soil biota.