The current study tested the contribution of native Acacia species of the Sudano-Sahelian zone to improving organic carbon and nitrogen level in Cambisols and Vertisols with specific focus on variation in microbial biomass (C mic), soil basal respiration (C resp) and metabolic quotient (qCO 2). The results show enrichment in total organic carbon (C total), in total nitrogen (N total) and higher clay content under Acacia canopies as compared to adjacent open grasslands. The relative nutrient concentration in Acacia cover showed an increase in C mic ranging from 203 to 572 μg g− 1 whereas in adjacent open grassland it varied from 100 to 254 CO 2–C μg g− 1. As a function of C mic (r= 0.60), C total (r= 0.70) and N total (r= 0.70), C resp was higher under Acacia canopies than open grassland and this difference was more pronounced when measured over lengthier incubation periods (10–21 days). A …