DESERT SYSTEM MICROBIAL BIOMASS DETERMINED BY PHOSPHOLIPID PHOSPHATE AND MURAMIC ACID MEASUREMENT

The effect of soil moisture on the biomass of the natural microbial co mmunities in the Negev Desert was studied during 1991-1993 using measu rements of phospholipid phosphate and muramic acid. The immediate resp onse of the microbial communities to varying amounts of nitrogen added as a single pulse was also studied. Two different weather conditions were observed during the study period: (1) the winter of 1992, which w as very cold and snowy, with intermittent rainfall occurring at the en d of winter and beginning of spring; (2) the winter of 1993 which was warmer, without snow, but with periodical rainfall occurring through e arly spring. Soil samples collected from the 0-10 cm and 10-20 cm dept hs during 1991-1992 showed significant changes in soil moisture and ph ospholipid phosphate and muramic acid concentrations following precipi tation events. The greatest concentration of phospholipid phosphate wa s observed in December 1991. The concentrations of phospholipid phosph ate at the two sample depths were 4-50 times greater than those found during other months. The concentration of muramic acid (31 . 19 mg g(- 1)) was greatest in March at 0-10 cm depth, as compared with the great est concentration (46 . 37 mg g(-1)) at 10-20 cm depth, which occurred in January. These muramic acid concentrations were 2-3 times greater than those found during other months. In 1992-93, soil samples were co llected from 0-10 cm depth areas amended with three different concentr ations of nitrogen (25, 50 or 100 kg NH4NO3 ha(-1)) and from unamended soil. Fluxes of the microbial communities (phospholipid phosphate and muramic acid) were correlated with the nitrogen treatments and diurna l fluctuations in soil moisture. The greatest concentrations of phosph olipid phosphate and muramic acid were found in soil treated with 50 o r 100 kg NH4NO3 ha(-1). Our results demonstrated that phospholipid pho sphate and muramic acid concentrations were greatest and more stable a fter nitrogen addition than in control soils lacking nitrogen amendmen ts. This paper demonstrates that the soil microbiota in the Negev Dese rt ecosystem are dependent on the moisture and nitrogen content of the soil and are influenced by seasonal variations in weather conditions, as well as by individual precipitation levels.