Biol Fertil Soils (2004) 39:415–421 DOI 10.1007/s00374-004-0723-9 ORIGINAL PAPER Einav Mayzlish · Yosef Steinberger Effects of chemical inhibitors on soil protozoan dynamics in a desert ecosystem Received: 30 May 2003 / Accepted: 10 December 2003 / Published online: 25 February 2004  Springer-Verlag 2004 Abstract This field study was designed to monitor the composition, size, and dynamics of the protozoan popu- lation during the different seasons in an arid environment. The protozoan population’s contribution to the ecological system was examined using chemical inhibitors. Samples were collected from the 0 to 10 and 10 to 20-cm depths from four different treatment plots: Nemacur (nemato- cide), Edigan (biocide), water, and control. The results obtained from the field study demonstrated that the number of protozoan individuals was affected by season and was significantly higher as spring neared. The flagellate population appeared in soil samples throughout the year, whereas the ciliate population appeared mainly during the wet seasons (winter and spring). Use of soil population inhibitors did not demonstrate any significant differences between treatments in the number of proto- zoan individuals in winter, summer, and autumn. During the population’s proliferation in spring, a significant change between treatments occurred in population com- position and size. Keywords Soil · Desert · Protozoa · Inhibitors Introduction According to Noy Meir (1973), biological processes in arid and semi-arid terrestrial ecosystems are triggered by water, which is one of the most limited and unpredictable factors in time, amount, intensity and space. Therefore, desert soils are constantly under extreme conditions of dryness that influence the availability of nutrients for plant and faunal activity (Ashraf and McNeilly 1994). According to Couteaux and Darbyshire (1998), the major part of the biogeochemical cycle takes place in the soil milieu triggered by biotic compartments. These critical nutrient transformations are facilitated by soil organisms such as bacteria, fungi, protozoa and nematodes living in the water films covering soil aggregates and filling pore spaces (Bamforth 1995; Swift and Anderson 1993). Studies undertaken in tropical ecosystems have elucidated the important role of the protozoan community in C and N cycles in grazing the bacteria (Couteaux and Darbyshire 1998). The protozoan population is known to be one of the most important bacterial feeders in soils, followed by bacteria-feeding nematodes. Due to their size, protozoa are able to move and utilize very small pore spaces unavailable to other soil biota (Bamforth 1995; Zwart and Brussaard 1991). Elliot et al. (1979) and Kuikman and Van Veen (1989) found that the nitrogen content of plants increases in the presence of protozoa, and that the grazing of bacteria and other microbial populations by protozoa resulted in improved availability of specific microbial N to plants. The mobility, feeding and growth of soil protozoa as aquatic organisms depends on their ability to cope in systems with extreme fluctuations in moisture levels, by their capability to encyst (Bryant et al. 1982). Alabouvette et al. (1981) estimated the generation time for protozoa to be 2–48 h, emphasizing the possible fast response triggered by favorable conditions. In desert systems where moisture, radiation, temperature, and organic matter limit abiotic parameters, biotic activity is determined by the “windows of activity-opportunity” triggered by moisture availability. Despite the importance of soil protozoa in unpredictable environments, there have been very few studies on their population dynamics. A study of selective chemical inhibitors was under- taken in order to be able to evaluate both the direct and indirect effects on the protozoa population in a desert system. The use of selective inhibitors has become an important research tool for identifying the importance of specific groups to soil stability (Colins et al. 1994). A selective reduction of a trophic population in the food web allows separation into the biotic components of the E. Mayzlish · Y. Steinberger ( ) ) Faculty of Life Sciences, Bar-Ilan University, 52900 Ramat-Gan, Israel e-mail: steinby@mail.biu.ac.il Tel.: +972-3-5318571 Fax: +972-3-5351824