Trends in Resin and KCl-extractable Soil Nitrogen Across Landscape Gradients in Taylor Valley, Antarctica

Abstract

Previous descriptions of soils in the McMurdo Dry Valleys, Antarctica, have focused on the dominance of abiotic controls rather than on nutrient cycling. Although free-living N₂-fixing and nitrifying microorganisms have been isolated in Antarctic soils, little is known about in situ nitrogen (N) cycling. We measured KCl-extractable NH₄ ⁺ and NO₃ ^–, as well as anion resin exchangeable NO₃ ^–, across sediment–soil transects and in two positions on a hill slope in Taylor Valley, Antarctica. These landscapes provide gradients of soil moisture, salinity, and texture that influence invertebrate communities and organic matter dynamics. Assuming an N cycle dominated by abiotic inputs, we hypothesized that inorganic N content would be predominantly comprised of NO₃ ^– and most strongly correlated to soil salinity, while NO₃ ^– flux (estimated by resin adsorption) would be most influenced by soil water content, salinity, and total soil NO₃ ^– concentrations. Our results were inconsistent with a physically dominated N cycle. In contrast to previous studies of Dry Valley soils, we found that NH₄ ⁺ made up a large proportion of inorganic N. Total KCl-extractable N was correlated most strongly with total soil N and soil moisture. The most saline soils in the swale of a hill slope had the highest concentrations of NO₃ ^–, but we found no overall correlation between soil salinity and resin-exchangeable NO₃ ^– or KCl-extractable N. Resin-extractable NO₃ ^– was most strongly correlated with total soil N, soil water content, and KCl-extractable NH₄ ⁺, suggesting that accumulation of NO₃ ^– in resins was influenced by the mineralization of organic matter and not strictly by ionic migration, as an abiotic-based model may have predicted. We conclude that biological N cycling is significant in some Dry Valley soils and that the dominance of biological vs physical influences over N cycling is controlled in part by the availability of soil moisture and organic matter.