Statistical learning and uncommon soil microbiota explain biogeochemical responses after wildfire

1 Abstract Wildfires are a perennial event globally and the biogeochemical underpinnings of soil responses at relevant spatial and temporal scales are unclear. Soil biogeochemical processes regulate plant growth and nutrient losses that affect water quality, yet the response of soil after variable intensity fire is difficult to explain and predict. To address this issue, we examined two wildfires in Colorado, USA across the first and second post-fire years and leveraged Statistical Learning (SL) to predict and explain biogeochemical responses. We found that SL predicts biogeochemical responses in soil after wildfire with surprising accuracy. Of the 13 biogeochemical analytes analyzed in this study, 9 are best explained with a hybrid microbiome + biogeochemical SL model. Biogeochemical-only models best explain 3 features, and 1 feature is explained equally well with hybrid or biogeochemical-only models. In some cases, microbiome-only SL models are also effective (such as predicting NH 4 + ). Whenever a microbiome component is employed, selected features always involve uncommon soil microbiota (i.e., the ‘rare biosphere’, existing at < 1% relative abundance). Here, we demonstrate that SL paired with DNA sequence and biogeochemical data predict environmental features in post-fire soils, though this approach could likely be applied to any biogeochemical system.