Abstract
The carob tree (Ceratonia siliqua L.), is a major component of the Mediterranean ecosystem, playing an important cultural and industrial role in the Mediterranean area. However, in recent decades the success rate of carob tree plantations has been declining, particularly under limited irrigation conditions. The conservation of this species is therefore highly dependent on our ability to improve its resistance to the worsening of drought periods. The use of arbuscular mycorrhizal fungi has been proposed as a promising strategy to improve the tolerance of the carob tree to cope with drought. However, mycorrhizae represent only a part of the beneficial microbiota for plant growth, and native microbial communities, for example associated with pioneer plants in the carob tree habitat, could represent beneficial microbial sources for the survival of the carob tree in a climate change context.The objectives of this work are (i) to characterise the soil microbiota in different habitats associated with the carob tree in Morocco, and to determine their specificity in relation to the major plant components, (ii) to assess their impact on the growth and resistance of the carob tree by using these soils as bio inoculants. The hypotheses are (i) that the soil microbiota is structured within a habitat by the associated floristic diversity and (ii) that the specificities ofthe soil and root microbiota are major determinants of the growth of the carob tree and its level of resistance to drought.The results showed a predominance of actinobacteria, proteobacteria and ascomycetes in two major carob tree habitats, characterised by functional divergences between North and South.The use as a bio-inoculant of the soil microbiota associated with different plant components of carob habitats has shown similar performances between the native carob microbiota and those associated with barley and white broom. By contrast, the native carob microbiota conferred little resistance to drought conditions, unlike that of the lentisk tree. Growth performance in non-water-limiting conditions could be linked to the joint action of mycorrhizae and rhizobia,while the improvement in drought resistance seems to be conferred mainly by the action of DSE (dark septate fungal endophytes), and potentially to mycorrhizae. The lenstik tree could be a promising target for improving carob tree resistance to drought by developing natural microbiote engineering (transplanting soil microbiotes or soil microbiote management by plant cover).