Fertilization of the desert soil by rock-eating snails

PLANT productivity in deserts can be nitrogen-limited. Nitrogen inputs are often low, soil nitrogen pools small, and losses from runoff, erosion, volatilization and denitrification, can be high^1-6. We have now found an unusual, important source of soil nitrogen in the Central Negev Highlands of Israel, a limestone rock desert with patches of soil (Fig. 1). Snails feed on endolithic lichens that grow within the rock, ingesting both rock and lichens^7,8, and depositing their faeces on the soil under the rocks. Snails transfer between 22-27 mg nitrogen per m² per year to soil, which constitutes about 11% of total soil nitrogen inputs, at least 18% of net soil inputs, and a minimum of 27% of the nitrogen annually accumulated by endolithic lichens from dust. The substantial contribution of snails to the nitrogen cycle is probably important for higher plant production.