Argan and pine stands comparably improve soil organic matter levels and microbiome structure and function under semi-arid Mediterranean conditions

Abstract

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 pine ( Pinus halepensis). Methods We assessed soil physicochemical properties, organic matter (SOM) characteristics (content, molecular composition and thermogravimetric fractions), priming effects, microbial activity, and metagenomics-based characterization of microbial communities under argan and pine stands, compared to adjacent bare soil. Results Both argan- and pine-influenced soils showed significantly higher SOM content (12.13% and 11.74%, respectively) than bare soil (4.51%), with comparable increases in organic carbon and nutrient availability. SOM characterization revealed that vegetation cover promoted higher SOM chemical diversity and a greater proportion of labile and intermediate SOM fractions, but differences between both types of trees were subtle. Both covers induced higher priming effects than bare soil, without compromising SOM accumulation. Argan and pine induced similar taxonomic shifts in the microbial community, with Solirubrobacter predominating under both tree species, whereas Rubrobacter dominated in bare soil. Functional profiles were largely conserved between argan- and pine-influenced soil compared to bare soil, with differences limited to 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, argan-influenced soil exhibited physicochemical and microbial properties comparable to those under pine, supporting argan as a potential alternative for reforestation and land restoration in Mediterranean ecosystems under increasing aridity.

Bibliographic Information