Pedobiologia 44, 591–608 (2000) © Urban & Fischer Verlag http://www.urbanfischer.de/journals/pedo 0031–4056/00/44/05–591 $ 12.00/0 Effects of increased nitrogen deposition on soil nematodes in alpine tundra soils E. Lokupitiya 1 , N. L. Stanton 1 , R. S. Seville 1 and J. R. Snider 2 1 Department of Zoology and Physiology and 2 Department of Atmospheric Science, University of Wyoming, Laramie, WY 82071 USA Accepted: 7. March 2000 Summary Because of anthropogenic activities, atmospheric deposition of nitrogen has increased on some high elevation ecosystems in North America. On Elk Mountain in SE Wyo- ming, USA, we found that ice, formed by the impaction of supercooled cloud dro- plets, contains nitrogen levels (NH 4 + = 58 ± 47 μmole/l, NO 3 - = 52 ± 40 μmole/l) signi- ficantly higher than snow (NH 4 + = 7 ± 5 μmole/l, NO 3 - = 14 ± 7 μmole/l). At this site the impaction process (riming) occurs on krummholz and is an important mechanism of water and nutrient deposition. We sampled nematodes in alpine soil for two seasons under this rime ice deposition and in adjacent meadow and krummholz soil with only snow deposition. No significant difference was found in nematode density and trophic composition between snow and rime ice deposition zones in krummholz; and nema- tode densities were significantly higher in meadow soil than in the krummholz rhi- zosphere. Densities of active nematodes were highest immediately after snow melt and a positive correlation was found between nematode density and percent soil moi- sture. With subsequent soil drying, nematodes gradually entered anhydrobiosis and this process began earlier in the exposed meadow than under the krummholz canopy. In a subsequent microcosm experiment we exposed nematodes in two alpine soils to four different nitrogen treatments [ammonium nitrate (NH 4 NO 3 ) at 0, 20, 40 and 80 kg N/ha/yr] and two temperatures (5 and 25°C). None of the three variables had a significant effect on nematode density. But at the first sampling (1 month) the inter- action between soil type and nitrogen level was significant, and at the second and final sampling (6 months) the interaction between soil type and temperature was sig- nificant. Nematode response to increasing nitrogen deposition rates varied in a com- Corresponding author: N. L. Stanton, e-mail: stanton@uwyo.edu