What fire didn’t take away: plant growth-promoting microorganisms in burned soils of old-growth Nothofagus forests in Los Andes Cordillera

Wildfires can dramatically alter forests, their biodiversity and goods they provide to society. In the Andes Cordillera, Nothofagus pumilio is a native, fire-sensitive tree species that is completely excluded from severely burned areas. Therefore, it is of interest to evaluate whether there are differences in the microbial soil communities that could contribute to improve the recruitment of N. pumilio after a fire. We aimed at determining the diversity of soil bacteria and fungi associated with Nothofagus pumilio in old-growth forests affected by a moderate severity wildfire in the Andes Cordillera of south-central Chile in 2015.

Eight years after fire, soil samples were collected from selected N. pumilio rhizosphere and bulk soil in fire-affected areas, and were compared with those from unburned areas using a metabarcoding approach.

We found that symbiotic microorganisms such as saprophytic, ectomycorrhizal fungi, ericoid mycorrhizal taxa and N-fixing bacteria were present with high abundances in the burned area. The most abundant bacterial genera were Mycobacterium, Rhodoplanes and Bryobacter. Meanwhile, Cortinarius and Penicillium were the most common fungal genera identified in burned and unburned sites.

Moderate severity wildfires in Nothofagus pumilio forests do not result in significantly different soil microbiomes eight years post-burn in either the rhizosphere or bulk soil, which could be key for N. pumilio establishment and survival after fire. Identifying the microbial diversity associated with native trees after fire is essential to know symbiotic microorganisms supporting the recovery of plant species.