Distribution of soil microbial biomass and free-living nematode population in terrace chronosequences of Makhtesh-Ramon crater

In this study, we examined the effects of the age of erosional fluvial terraces of Makhtesh Ramon (Roman crater) in the central Negev Desert on soil chemical and biological properties. There were significant effects of erosion age of these terraces on soil moisture, organic carbon, soil salinity, and electrical conductivity. It is known that soil biological activity in arid ecosystems is determined by well-known limiting factors such as soil moisture and organic matter. Significant (P < 0.002) differences in total nematode population and microbial biomass [(22.0-3.4 C_mic (μg C g ^-1 soil)] were observed between terraces. Biological activity of soils in lower and younger terraces was greater than in older and higher terraces. The ecophysiological status (qCO₂) of the soil microbial community was found to decrease from a maximal value of 1.3 to 0.32 mg CO ₂-C (gC_mich)^-1 along the terraces (from younger to older ones). This study illustrates the integrated effect of age, altitude, and the morphostratigraphic position of terraces on the biological activity of soils.