Bacterial Products and Their Effect on the Shrubby Legume Calicotome villosa (Poir.) Link

Calicotome villosa is a eurioic legume with broad distribution in the south of Europe. It can grow in almost any type of soil as well as in humid and dry and nutrient-deficient ecosystems. The broad distribution and eurioic nature of C. villosa may be attributed to its ability to establish endophytic associations with plant-growth-promoting (PGP) bacteria housed in the nodules and rootlets. This study examined the legume–microbe interaction of C. villosa growing in two contrasting locations: a hilltop with high sun irradiance and drought, and a valley bottom with a low level of radiation and sufficient soil humidity for plant growth. Calicotome villosa adult plants established endophytic interactions with bacteria in six genera: Pseudomonas, Stenotrophomonas, Bacillus, Paenibacillus, Brevicacterium, and Rhizobium. Plants growing on the hilltop had associated lower bacterial richness than those grown on the valley bottom. All strains were drought-tolerant and produced siderophores, IAA, HCN, and NH3 that stimulated plant performance in C. villosa plants and the other four legumes commonly present in the understory of the shrub communities. The legumes’ capacity to selectively host symbiotic bacteria that enhance plant survival in harsh conditions partly accounts for the diverse partnerships between C. villosa plants and their symbionts, ultimately explaining the wide distribution of this plant species.