Bacterial and fungal dynamics and their contribution to microbial biomass in desert soil

The effect of soil moisture on the bacterial and fungal contribution to the soil microbial biomass was studied in the Negev Desert during 1991-1992. Two important features of the rainfall were observed during this period: (1) a strongly clustered series of peaks at the beginning of January and February with snow and low temperatures; and (2) low and intermittent rainfall during the end of winter and early spring. Wetting of the dry desert soil triggered a rapid response of microbial activity which resulted in a significant increase in the soil microbial biomass. In the 0-10 cm layer, changes in soil moisture during the wet season occurred more regularly and the fungal biomass was significantly (p < 0.05) higher than the bacterial biomass. In the 10-20 cm soil layer, the opposite picture was obtained and the bacterial biomass significantly exceeded the fungal biomass (p < 0.05). Our results suggest that in the Negev Desert ecosystem, which is characterized by scattered rainfall events, significant differences in detritus food web composition will occur in the different soil layers in a wet year. (C) 1997 Academic Press Limited.