Effects of Soil Abiotic and Biotic Factors on Tree Seedling Regeneration Following a Boreal Forest Wildfire

Abstract

Wildfire disturbance is important for tree regeneration in boreal ecosystems. A considerable amount of literature has been published on how wildfires affect boreal forest regeneration. However, we lack understanding about how soil-mediated effects of fire disturbance on seedlings occur via soil abiotic properties versus soil biota. We collected soil from stands with three different severities of burning (high, low and unburned) and conducted two greenhouse experiments to explore how seedlings of tree species (Betula pendula, Pinus sylvestris and Picea abies) performed in live soils and in sterilized soil inoculated by live soil from each of the three burning severities. Seedlings grown in live soil grew best in unburned soil. When sterilized soils were reinoculated with live soil, seedlings of P. abies and P. sylvestris grew better in soil from low burn severity stands than soil from either high severity or unburned stands, demonstrating that fire disturbance may favor post-fire regeneration of conifers in part due to the presence of soil biota that persists when fire severity is low or recovers quickly post-fire. Betula pendula did not respond to soil biota and was instead driven by changes in abiotic soil properties following fire. Our study provides strong evidence that high fire severity creates soil conditions that are adverse for seedling regeneration, but that low burn severity promotes soil biota that stimulates growth and potential regeneration of conifers. It also shows that species-specific responses to abiotic and biotic soil characteristics are altered by variation in fire severity. This has important implications for tree regeneration because it points to the role of plant–soil–microbial feedbacks in promoting successful establishment, and potentially successional trajectories and species dominance in boreal forests in the future as fire regimes become increasingly severe through climate change.

Direct and indirect effects of fire on microbial communities in a pyrodiverse dry‐sclerophyll forest

“…Microbial communities can facilitate the recovery of all other life-forms after disturbance (Claridge et al, 2009;Selosse et al, 2006). The influence of fire on microbial communities can be direct; through the combustion of live biomass, or indirect; through influencing plant-soil-microbial interactions (Barnes et al, 2017;Ibáñez et al, 2021;van der Putten et al, 2013;Wardle et al, 2004), and these effects vary with fire intensity and frequency, and the interactions among them (Dooley & Treseder, 2012;Muñoz-Rojas et al, 2016;Pérez-Izquierdo et al, 2021;Shen et al, 2015). For instance, during a high-intensity fire, soil temperatures can exceed 500°C, which can rapidly volatilise nutrients and combust organic matter and its resident microflora, including leaf litter on the soil surface (Certini, 2005;Granged et al, 2011).…”

Playing with FiRE: A genome resolved view of the soil microbiome responses to high severity forest wildfire

“…During severe wildfires, the soil microbiome can be impacted directly due to heating killing heat-sensitive microbial taxa or indirectly via lasting changes in soil chemistry (e.g., pH, organic matter structure) that continue to influence soil microbiome assembly 16 . Wildfires reduce soil microbial community diversity in numerous ecosystems [17][18][19][20] and such changes are likely to influence and potentially inhibit post-fire plant recovery 21,22 . Although post-fire shifts in soil microbiome composition are relatively well characterized across ecosystems 16,18,19,23 , the impacts of fire on microbiome metabolic function and microbiallymediated biogeochemical processes are not.…”

Wildfire-dependent changes in soil microbiome diversity and function

“…During wildfires, the soil microbiome can be impacted immediately by the loss of heat-sensitive taxa and thereafter by lasting changes in soil chemistry and vegetation shifts 12 . Wildfires reduce soil microbial biomass and community diversity in numerous ecosystems [13][14][15][16] and such changes probably influence and inhibit post-fire plant recovery 17 .…”