Microbial biomass and activity in alkalized magnesic soils under arid conditions

Microbial biomass, indices of microbial activity and the activities of the hydrolases negatively correlated with Mg2+/Ca2+ or exchangeable Mg2+ percentage. Biomass C, biomass N, microbial quotient (the percentage of soil organic C present as biomass C), biomass N as a percentage of total N, potentially mineralizable N, FDA hydrolysis rate and arginine ammonification rate decreased exponentially with increasing EC. The biomass C/N tended to be lower in soils with higher salinity and Mg2+ alkalinity, probably reflecting the bacterial dominance in microbial biomass in alkalized magnesic soils. The metabolic quotient (qCO2) positively correlated with salinity and Mg2+ alkalinity, and showed a quadratic relationship with EC, indicating that increasing salinity and Mg2+ alkalinity resulted in a progressively smaller, more stressed microbial communities which was less metabolically efficient. Consequently, our data suggest that salinity and Mg2+ alkalinity are stressful environments for soil microorganisms.