Microbial succession dynamics along glacier forefield chronosequences in Tierra del Fuego (Chile)

Following the retreat of a glacier, microbial colonization paves the way for future plant successions as nutrients are gradually introduced into the ecosystem. Characterizing the dynamics of this initial microbial colonization process is a key to understanding how these rapidly receding glacier areas are colonized. This study examines primary successions of bacteria, fungi and algae in two glacier forefields chronosequences on opposite slopes of Cordillera Darwin (Tierra del Fuego, Chile). Both slopes (southern and northern) show contrasting climate factors along with rapid rates of plant succession. Through a high-throughput sequencing approach, we identified Cyanobacteria as the dominant bacteria in younger soils close to the glacier terminus, whereas abundances of Alphaproteobacteria and Acidobacteria increased with soil surface age. Lichen-forming fungi and parasitic fungi were the most abundant fungal groups in younger succession stages, while saprophytic and mycorrhizal orders dominated later stages. The order Prasiolales predominated algal communities close to the glacier terminus, while Microthamniales and Chlamydomonadales orders dominated subsequent succession stages. Our observations reflect a changing community structure over time of the three microbial groups examined, and the replacement of taxa during the succession. Changes in composition are especially marked between the youngest succession states and subsequent ones in both forefields. Simultaneous analysis of bacterial, fungal and algal communities revealed the different trajectories of the three groups, with bacterial and fungal communities showing more marked succession patterns. Our results point to more relevant roles for bacteria at the initial stages of succession, while fungi could play a dominant role over bacteria as succession progresses. The ubiquity of algal taxa along the chronosequences was also observed. The two glacier forefields showed different microbial temporal dynamics, indicating that local factors affect the rate of microbial community assembly and, consequently, drive the primary succession process.