Evaluation of Density and Viability of Arbuscular Mycorrhizal Spores in Austrocedrus chilensis Forests Affected by Wildland Fires in Patagonia, Argentina

Background: Wildfires represent a recurrent disturbance in the Patagonia Andean region, with increasing frequency in recent decades. Austrocedrus chilensis is an arbuscular mycorrhizal (AM) endemic conifer that is particularly vulnerable to fire, a situation that will worsen with climate change. In February 2015, a wildfire affected 5700 ha of Austrocedrus chilensis forests with varying severities (WFSs). The aim of this study was to determine and compare the density of AM spores (AMSs) in soil affected by different WFS and non-affected sites, considering site features. Methods: Ninety soil samples were collected from three sites 10 months and 5 years after the fire. The AMSs density was determined, a bioassay was set, and soil physicochemical features were evaluated. Results: After the wildfires, spores were significantly more abundant in sites affected by moderate severity fires. After 5 years, burned sites showed no differences between severities, but the driest sites showed no changes since the wildfires occurred. Seedlings from the bioassay showed less than 25% mycorrhizal colonization growing in soil from burned sites, regardless of fire severity, compared with unburned soils. Conclusions: For restoration strategies, it must be considered that wildfires reduce mycorrhizal spores and mycelium and alter soil properties, indicating that both WFSs require active restoration; under drier conditions, the spore banks do not change after a 5-year period.