Oasis management and topography interactively shape soil inorganic carbon dynamics in hyper-arid soils

Soil inorganic carbon (SIC) constitutes a major component of total soil carbon in arid and hyper-arid regions and plays an important role in terrestrial carbon storage. SIC originates from both lithogenic and pedogenic carbonates formed through coupled biological–geochemical processes. However, the extent to which oasis management influences SIC dynamics remains unclear, particularly under potentially acidifying conditions associated with fertilisation and enhanced biological activity. We investigated SIC dynamics in southwestern Tunisia by sampling soils to 120 cm depth across three traditional and three modern oasis systems, along topographic gradients and under contrasting tree microsites. SIC accounted for 76% (median) of total soil C across all samples, confirming its dominance under hyper-arid conditions. SIC contents and stocks (mean: 31.3 kg m −2 ) were not significantly affected by oasis management or tree position. Instead, SIC patterns were structured by interactions among management, topography, and soil depth. Along the catena, SIC declined downslope in modern oases but increased downslope in traditional systems, highlighting context-dependent topographic organization rather than uniform management effects on SIC dynamics. Carbon isotopic signatures (δ 13 C-SIC) and isotope mixing models indicated that 20–40% of SIC was derived from soil-respired CO 2 , with higher contributions in traditional oasis systems and surface soils. The negative relationship between δ 13 C-SIC and SOC further supports coupling between organic and inorganic carbon pools. Overall, our results indicate that SIC dynamics in oasis systems are strongly buffered by geological and hydrological controls, while management primarily influences carbonate cycling and source partitioning rather than total SIC storage.