Response of the soil microbial biomass and nematode population to a wetting event in nitrogen-amended Negev desert plots

Water and N availability are the major limiting factors of primary production in desert ecosystems, and the response of soil biota to these two factors is of great importance. We examined the immediate response of soil nematodes and the microbial biomass to a single pulse of water amendment in N-treated plots in the Israeli Negev desert. Plots were treated with 0, 50 and 100 kg NH4NO3 ha(-1) in December 1992, and at the end of the summer period (August 1993) the plots were exposed to a 15 mm water. Soil samples from the 0-10 cm layer were collected daily and analysed soil moisture, total soluble N, nematode populations and microbial biomass. Soil moisture increased to 8.5%, then gradually decreased to 2% during the 11 days of the study. Microbial biomass, soil respiration and metabolic quotient values did not exhibit any significant correlation with soil N levels. Free-living nematode population levels in the different plots were found to increase from a mean level of 45500 to a mean level of 92300 individuals m(-2). N treatment was found to affect the patterns of free-living nematode population dynamics. The results of this study demonstrated the importance of moisture availability levels and the ability to mobilize previous N inputs into available N which, occurring in pulses, can affect the microbial ecophysiological status, nematode population dynamics and the interrelationship between these two important components in the desert soil milieu.