Title: Soil-Parent Material and Land Use Effects on Sub-Soil Properties in Northern Tunisia: Evidence from the Tunisian SUS-SOIL Living Lab

Soil is a vital component of the Earth, providing essential ecosystem services related to biodiversity, plant growth, agricultural production, carbon sequestration, and environmental quality. However, geodiversity, including geology, geomorphology, and sediments, remains underrepresented in conventional ecosystem service frameworks. The SUS-SOIL is a 4-year project, develops 15 Subsoil-Living Labs, including Tunisia. Aims to apply a harmonized soil sampling methodology to assess how parent material and land use influence soil properties, aiming to disentangle geological controls from land-use and management effects across contrasting lithological settings.

In Tunisia, study sites are located in the north where agricultural, forest, and urban land uses occur in close spatial proximity under comparable topographic conditions. Sites were selected on Oligocene, Mio-Pliocene, and Quaternary parent materials, enabling assessment of lithological controls on soil development in a Mediterranean semi-arid to sub-humid context. Agricultural systems include annual crops, permanent crops, and grasslands, while forest sites comprise natural and managed coniferous and broadleaved stands, complemented by urban soils from parks and home gardens.

Soil sampling is conducted to a maximum depth of 1 m using a composite protocol that distinguishes the plow layer (0-20 cm), consistent with the EU-LUCAS framework, from underlying organic and mineral subsoil horizons. The methodology integrates physico-chemical analyses (texture, bulk density, compaction, water retention, pH, electrical conductivity, cation exchange capacity, carbon, nitrogen, and phosphorus) with microbiological indicators of soil functioning and ecotoxicology.

In Tunisia, 120 agricultural sites, 72 forest sites, and 12 urban sites were selected based on three main parent rock types to ensure geological diversity and comparability. Additional criteria included the close spatial proximity of contrasting land uses under identical topography, site accessibility, and the long-term availability of land for experiments investigating subsoil impacts on crop production.

Recent investigations in northwest Tunisia demonstrate that parent material and land use strongly control soil physical and chemical properties. Detailed profiling of representative soils-Luvisols, Cambisols, Vertisols, and Fluvisols-across contrasting lithologies highlights substantial variation in texture, carbonate content, organic matter distribution, and nutrient dynamics linked to geology and land use. For instance, Luvisols and Fluvisols developed on different parent rocks exhibit distinct horizon characteristics and fertility potentials. Alluvial Fluvisols show higher natural fertility but require careful water management, while clay-rich Luvisols are more susceptible to erosion due to their structure and lower organic inputs under certain uses. Complementary micronutrient analyses indicate that boron distribution in forest and agricultural soils varies with texture, organic matter, and depth, with forest soils showing higher available B in deeper layers, while agricultural soils derived from sedimentary rocks exhibit higher total B content.

The Tunisian case study highlights the importance of understanding soil-parent material interactions in the southern Mediterranean. It provides guidance for developing site-specific soil management strategies under increasing climatic pressures.

Funding: This study was supported by the SUS-SOILproject funded by the European Union GA 101157560. Views and opinions expressed are of the author(s) only and do not necessarily reflect those of the European Union. Neither the European Union nor the granting authority can be held responsible for them.