Release and consumption of nitrogen by snail feces in Negev Desert soils

Snail grazing and feces production have been shown to be major components of the nitrogen (N) budget of Negev Desert ecosystems. However, the movement of N from feces into soil N cycling processes has not been studied. In this study, we measured immediate N release from different types of snail feces following wetting of dry desert soils, and characterized potential net N mineralization and nitrification and soil respiration over a 12-day incubation under laboratory conditions. The dynamics of inorganic N exhibited two distinct phases during the 12-day incubation: (1) immediate release of inorganic N following wetting of the soil and (2) decline of inorganic N from day 1 to day 12 of the incubation. The immediate pulse of N release from this one wetting event (6-25 mg N m(-2)) was larger than annual atmospheric inputs of N to Negev Desert ecosystems (<2 mg N m(-2)); however, from 50 to 80% of the N released upon wetting was consumed by the end of the incubation. There were differences in inorganic N release and respiration from feces from different kinds of snails, and from feces from the same species of snail fed different plants. The results suggest that while snail feces contribute significant amounts of plant available N to Negev ecosystems, plants must compete with other ''sinks'' for this N.