干旱区生态环境知识资源中心

The effect of soil moisture on the biomass of the natural microbial communities in the Negev Desert was studied during 1991-1993 using measurements of phospholipid phosphate and muramic acid. The immediate response 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 was very cold and snowy, with intermittent rainfall occurring at the end of winter and beginning of spring; (2) the winter of 1993 which was warmer, without snow, but with periodical rainfall occurring through early spring.

Soil samples collected from the 0-10 cm and 10-20 cm depths during 1991-1992 showed significant changes in soil moisture and phospholipid phosphate and muramic acid concentrations following precipitation events. The greatest concentration of phospholipid phosphate was observed in December 1991. The concentrations of phospholipid phosphate 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 greatest 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 collected from 0-10 cm depth areas amended with three different concentrations 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 diurnal fluctuations in soil moisture.

The greatest concentrations of phospholipid phosphate and muramic acid were found in soil treated with 50 or 100 kg NH4NO3 ha(-1).

Our results demonstrated that phospholipid phosphate and muramic acid concentrations were greatest and more stable after nitrogen addition than in control soils lacking nitrogen amendments.

This paper demonstrates that the soil microbiota in the Negev Desert 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.