Rhizosphere effect of three plant species of environment under periglacial conditions (Majella Massif, central Italy)

The chemical, physical and biological processes occurring in the rhizosphere can influence plant growth by modifying root associated microorganisms and nutrient cycles. Although rhizosphere has been widely investigated, little is known about the rhizosphere effect of pioneer plants in soils of periglacial environments. The knowledge of the processes controlling soil-plant relationships in these severe environments may help understanding the ecological evolution of newly deglaciated surfaces. We selected three plants [. Helianthemum nummularium (L.) Mill. subsp. grandiflorum (Scop.), Dryas octopetala (L.), and Silene acaulis (L.) Jacq. subsp. cenisia (Vierh.) P. Fourn.] that sparsely occupy deglaciated areas of central Apennines (Italy), with the aim to assess changes between rhizosphere and bulk soil in terms of physical, chemical, and biological properties. The three plants considered showed to have different rhizosphere effect. Helianthemum induced a strong rhizosphere effect through a synergistic effect between root activity and a well adapted rhizosphere microbial community. Dryas did not foster a microbial community structure specifically designed for its rhizosphere, but consumes most of the energetic resources supplied by the plant to make nutrients available. Conversely to the other two species, Silene produced slight soil changes in the rhizosphere, where the microbial community had a structure, abundance and activity similar to those of the bulk soil. The ability to colonize harsh environments of Silene is probably linked to the shape and functions of its canopy rather than to a functional rhizosphere effect.This study showed that the rhizosphere effect differed by species also under high environmental pressure (periglacial conditions, poorly developed soil), and the activity of roots and associated microbial community is decisive in modifying the soil properties, so to create a suitable environment where plants are able to grow.