Rhizosphere fungal assemblages and soil enzymatic activities in a 110-years alpine chronosequence

• Plant species affected AMF and ECM fungal communities in a young alpine ecosystem.
• Soil developmental stage determined the community composition of saprophytic fungi.
• Rhizosphere from Salix helvetica had high chitinase and α-glucosidase activities.
• Rhizosphere from Rhododendron ferrugineum had high α-glucosidase and sulfatase activities.
• Rhizosphere from Agrostis gigantea had high phosphatase and β-glucosidase activities.

The abundance, distribution and functions of soil fungi in alpine ecosystems remain poorly understood. We aimed at linking the fungal community structure with soil enzymatic activities in the rhizospheres of several plants associating with mycorrhizal fungi (arbuscular, ecto- and ericoid) and growing along a soil developmental gradient on the forefield of an alpine glacier. Fungal communities in roots and in rhizosphere soils were assessed using a site-tailored set of quantitative PCR assays with fluorescent hydrolysis probes. Enzymatic activities of mycorrhizal roots and rhizosphere soils were assessed using fluorogenic substrates. In this study we addressed: i) whether and how the structure of fungal communities and enzymatic activities in rhizosphere soils change along the soil developmental gradient, ii) whether the type of mycorrhiza shows a clear relationship to the pattern of enzymatic activities in the rhizosphere, and iii) how the structure of fungal communities and enzymatic activities in rhizosphere soils is related to plant species abundances along the soil chronosequence. The results suggest that plant identity affected the structure of both ecto- and arbuscular mycorrhizal fungal communities in rhizosphere soil and roots, whereas the community of non-mycorrhizal fungi was rather dictated by the soil developmental stage. Both plant identity and associated mycorrhizal fungi affected the enzymatic activity in the rhizosphere soil. Species-specific elevations of rhizosphere enzyme activities were detected for Salix helvetica (chitinase and α-glucosidase), Rhododendron ferrugineum (α-glucosidase and sulfatase), and Agrostis gigantea (phosphatase and xylosidase). These results indicate different functional roles played by different types of mycorrhizal symbiosis in a young alpine ecosystem.