Can Permanganate Oxidizable Carbon, Microbial Respiration, and Carbon Mineralization Rate Reflect Carbon Dynamics Across Land Use and Pedo-climate Gradients in West African Semi-Arid Zones?

Gannouka Nadjire^1*Alimata Arzouma Bandaogo²Amanuel W Gebremichael³Oumarou Ouedraogo¹Joseph Issaka Boussim¹

• ¹Laboratoire de Biologie et Ecologie Végétales, Université Joseph KIZERBO, Ouagadougou, Burkina Faso
• ²Institut de l'Environnement et de la Recherche Agricole,, Ouagadougou, Burkina Faso
• ³GFZ Helmholtz-Zentrum fur Geoforschung, Potsdam, Germany

Climate variability, soil type, land use, and vegetation structure modulate soil carbon dynamics, but their effects on sensitive soil carbon indicators are not adequately quantified in semi-arid ecosystems. This study investigated the separate and combined impacts of pedo-climate, land use, and canopy cover on permanganate oxidizable carbon (POXC), soil microbial respiration (CO₂-C), and potential carbon mineralization rate (CMR) in West African semi-arid drylands, evaluating their utility as carbon dynamics indicators. We collected 480 composite soil samples across Sudanian and Sudano-Sahelian zones, covering three land use types (cropland, fallow, protected area), two canopy positions (subcanopy, intercanopy), and two depths (0-10 cm, 10-30 cm). POXC, CO₂-C, and soil organic carbon concentrations were analyzed, and CMR was derived from CO₂-C per unit SOC. The indicators exhibited distinct sensitivities, with POXC responding primarily to pedo-climate and canopy cover. CO₂-C was influenced by all factors with depth-amplified variation, and CMR was most sensitive to land use and canopy position in topsoil but shifted to pedo-climatic control at depth. The fixed effects explained a small portion (14% to 16%) of layer 0-10 cm POXC, CO2-C, and CMR variance, indicating there a significant unmeasured variability sources. Depth moderated indicator relationships: POXC–SOC correlations weakened with depth, whereas CO₂-C–CMR associations strengthened, indicating a transition from surface labile carbon control to deeper microbial and nutrient constraints. Critically, the indicators provide complementary, depth‑explicit information: POXC and SOC contextualize pool size and labile availability, whereas CO₂‑C and CMR are used to assess the functional accessibility and energetic feasibility of decomposition, especially in subsurface soils where protection and quality constrain activity beyond carbon quantity. Therefore, these metrics are best used jointly to signal early changes and constrain decomposition processes within calibrated systems, rather than as stand-alone indicators of SOC dynamics in semi-arid regions. Further work should identify additional drivers to enhance capacity across depths and contexts.