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 producti on in desert ecosystems, and the response of soil biota to these two factor s is of great importance. We examined the immediate response of soil nemato des and the microbial biomass to a single pulse of water amendment in N-tre ated plots in the Israeli Negev desert. Plots were treated with 0, 50 and 1 00 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 solub le N, nematode populations and microbial biomass. Soil moisture increased t o 8.5%, then gradually decreased to 2% during the 11 days of the study. Mic robial biomass, soil respiration and metabolic quotient values did not exhi bit any significant correlation with soil N levels. Free-living nematode po pulation levels in the different plots were found to increase from a mean l evel of 45500 to a mean level of 92300 individuals m(-2). N treatment was f ound to affect the patterns of free-living nematode population dynamics. Th e results of this study demonstrated the importance of moisture availabilit y levels and the ability to mobilize previous N inputs into available N whi ch, occurring in pulses, can affect the microbial ecophysiological status, nematode population dynamics and the interrelationship between these two im portant components in the desert soil milieu.