Soil moisture integrates the influence of land-use and season on soil microbial community composition in the Ethiopian highlands

Conversion of old-growth natural forest to crop land or grazing land and then to eucalyptus plantation is prevalent under the present socio-economic conditions in Ethiopia. To investigate the soil microbial and soil bio-chemical properties among the different land-use types in the highlands of the Northeastern Ethiopia, we measured soil microbial biomass and the potential activities of six extracellular enzymes. The soil microbial biomass was higher in natural forest than in plantation and grazing land, which was explained by the higher soil C concentrations. The microbial C:N ratio was higher in the dry (C:N 11-19) than in the wet season (C:N 5-10), indicating more fungal biomass in the dry season. The strong positive correlation between the microbial C:N ratio and chitinase activity supports the interpretation that the microbial C:N ratio reflects the dominance between fungi and bacteria in soil. The C:N ratio was negatively correlated with soil moisture within and between seasons, indicating that soil moisture considerably influenced the microbial community. Our study demonstrated that land-use affects soil microbial properties and enzyme activity. Nonetheless, the increase in the microbial C:N ratio after land-use change is driven mainly by soil moisture (which is influenced by land use) rather than by changes in vegetation or soil properties.