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.

野火干扰对北方生态系统中的树木再生很重要。已经发表了大量关于野火如何影响北方森林再生的文献。然而，我们缺乏对土壤介导的火灾干扰对幼苗的影响如何通过土壤非生物特性与土壤生物群发生的了解。我们从具有三种不同燃烧程度（高、低和未燃烧）的林分收集土壤，并进行了两次温室实验，以探索树种（桦木、樟子松和冷杉）的幼苗如何) 在活土壤和由三种燃烧严重程度中的每一种的活土壤接种的无菌土壤中进行。在活土中生长的幼苗在未燃烧的土壤中生长最好。当用活土重新接种经过消毒的土壤时，冷杉和樟子松的幼苗在来自低燃烧严重程度林分的土壤中比来自高严重程度或未燃烧林分的土壤中生长得更好，这表明火灾干扰可能有利于针叶树的火后再生部分原因是土壤生物群在火灾严重程度较低时持续存在或火灾后迅速恢复。桦木对土壤生物群没有反应，而是由火灾后非生物土壤特性的变化驱动。我们的研究提供了强有力的证据，表明高火灾严重程度会产生不利于幼苗再生的土壤条件，但低火灾严重程度会促进土壤生物群，从而刺激针叶树的生长和潜在再生。它还表明，对非生物和生物土壤特性的物种特异性反应会因火灾严重程度的变化而改变。这对树木再生具有重要意义，因为它指出了植物 - 土壤 - 微生物反馈在促进成功建立中的作用，以及未来随着气候变化导致火灾状况变得越来越严重时北方森林中潜在的演替轨迹和物种优势。