Reforestation with argan performs equally to pine in improving soil organic matter levels and microbiome structure and function under semi-arid Mediterranean conditions

Background and aims Reforestation is widely promoted to mitigate soil degradation and desertification in semi-arid Mediterranean regions under future climate-change scenarios. The argan tree ( Argania spinosa ), a drought-resistant species, has been proposed as a potential alternative to Pinus halepensis , traditionally used in reforestation programs. Methods We assessed soil physicochemical properties, organic matter (SOM) content and composition, microbial activity, and the taxonomic and functional potential of microbial communities (using shotgun metagenomics) under argan and pine stands, compared to adjacent bare soil. Results Both argan- and pine-influenced soils showed significantly higher SOM (7.07% and 5.86%, respectively) than bare soil (1.91%), with comparable increases in organic carbon and nutrient availability. Vegetation induced marked shifts in microbial composition; Solirubrobacter increased in argan-influenced soil, while Rubrobacter dominated bare soil. Although microbial functional profiles were largely conserved, argan-influenced soil showed slight enrichments in glycan and amino acid metabolism pathways. Genes for inorganic phosphorus solubilization predominated in bare soil, whereas organic phosphorus mineralization pathways were more prevalent in vegetated soil. Conclusion Overall, soil under argan exhibited physicochemical and microbial properties comparable to those under P. halepensis , supporting A. spinosa as a viable alternative for reforestation and land restoration in Mediterranean ecosystems under increasing aridity.