RELEASE AND CONSUMPTION OF NITROGEN BY SNAIL FECES IN NEGEV-DESERT SOILS

Snail grazing and feces production have been shown to be major compone nts of the nitrogen (N) budget of Negev Desert ecosystems. However, th e 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 chara cterized potential net N mineralization and nitrification and soil res piration over a 12-day incubation under laboratory conditions. The dyn amics of inorganic N exhibited two distinct phases during the 12-day i ncubation: (1) immediate release of inorganic N following wetting of t he soil and (2) decline of inorganic N from day 1 to day 12 of the inc ubation. 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 Ne gev 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. The re were differences in inorganic N release and respiration from feces from different kinds of snails, and from feces from the same species o f snail fed different plants. The results suggest that while snail fec es contribute significant amounts of plant available N to Negev ecosys tems, plants must compete with other ''sinks'' for this N.