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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 (Cmic), soil basal respiration (Cresp) and metabolic quotient (qCO2). The results show enrichment in total organic carbon (Ctotal), in total nitrogen (Ntotal) and higher clay content under Acacia canopies as compared to adjacent open grasslands. The relative nutrient concentration in Acacia cover showed an increase in Cmic ranging from 203 to 572 μg g−1 whereas in adjacent open grassland it varied from 100 to 254 CO2–C μg g−1. As a function of Cmic (r = 0.60), Ctotal (r = 0.70) and Ntotal (r = 0.70), Cresp was higher under Acacia canopies than open grassland and this difference was more pronounced when measured over lengthier incubation periods (10–21 days). A lower qCO2 under Acacia cover (except for one site) demonstrated a change in microorganisms communities structure and higher substrate use efficiency as compared to open grassland. The results also show that soil texture, as well as vegetation cover, influenced microbial processes. The negative correlation between clay content and carbon mineralization (Cresp/Ctotal, qCO2), and positive linear relation between clay and Cmic supported the hypothesis that finer soil texture protects soil microbial biomass against degradation and limits organic matter mineralization. The specific effects of soil typology and vegetation cover on Cmic and qCO2 variability were significant, but the greater effects were attributed to vegetation cover. |
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