Distinct fungal successional trajectories following wildfire between soil horizons in a cold‐temperate forest

Abstract

Summary Soil fungi represent a major component of below‐ground biodiversity that determines the succession and recovery of forests after disturbance. However, their successional trajectories and driving mechanisms following wildfire remain unclear. We examined fungal biomass, richness, composition and enzymes across three soil horizons (Oe, A1 and A2) along a near‐complete fire chronosequence (1, 2, 8, 14, 30, 49 and c. 260 yr) in cold‐temperate forests of the Great Khingan Mountains, China. The importance of soil properties, spatial distance and tree composition were also tested. Ectomycorrhizal fungal richness and β‐glucosidase activity were strongly reduced by burning and significantly increased with ‘time since fire’ in the Oe horizon but not in the mineral horizons. Time since fire and soil C : N ratio were the primary drivers of fungal composition in the Oe and A1/A2 horizons, respectively. Ectomycorrhizal fungal composition was remarkably sensitive to fire history in the Oe horizon, while saprotroph community was strongly affected by time since fire in the deeper soil horizon and this effect emerged 18 years after fire in the A2 horizon. Our study demonstrates pronounced horizon‐dependent successional trajectories following wildfire and indicates interactive effects of time since fire, soil stoichiometry and spatial distance in the reassembly of below‐ground fungal communities in a cold and fire‐prone region.

Crown‐fire severity is more important than ground‐fire severity in determining soil fungal community development in the boreal forest

“…The total fungal biomass as well as the relative abundance and richness of symbiotic ectomycorrhizal fungi declined with increasing crown‐fire severity (Table 1). The ectomycorrhizal fungal genera Cortinarius and Russula that were abundant in the unburned stands were absent or of low abundance in all burned stands, in line with previous studies on fire chronosequences in boreal and hemi‐boreal forests (LeDuc et al., 2013; Sun et al., 2015; Visser, 1995; Yang et al., 2020). In particular, Cortinarius species are specialized in the mobilization of organic N (Bödeker et al., 2014) and form large individuals that are likely to demand large quantities of host C. Moderate‐ to high‐intensity fires convert part of the soil organic N to inorganic forms (Certini, 2005; Grogan et al., 2000), supposedly favouring disturbance‐adapted ectomycorrhizal fungi with high affinity for inorganic N and lower C demand (LeDuc et al., 2013).…”

“…and Laccaria oblongospora , recognized as pioneers in burned areas (Danielson, 1984; de Román & de Miguel, 2005), were not detected in the unburned stands but proliferated only after fire, probably from a sparse spore bank inoculum. In the mineral soil, the richness of ectomycorrhizal fungi was not significantly lower in the burned sites than in the unburned reference stands, and not related to tree mortality (Table 1), suggesting that the mineral soil may constitute a reservoir of ectomycorrhizal diversity, which may be of particular importance for post‐fire seedling regeneration in stands where the ectomycorrhizal fungal communities in the mor layer are severely damaged (Dahlberg, 2002; Yang et al., 2020).…”

“…Correlation between Bray-Curtis pairwise distances of fungal communities in the organic mor layer of logged and unlogged burned plots from the same stand and crown-fire severity index as analysed by GLMs n e e w t e b y t i r a l i m i s s i d d n a d e g g o l n u d e g g o l p lots post-fire chronosequences, ectomycorrhizal fungal richness has been found to increase linearly, concurrent with the recovery of above-ground vegetation (Duhamel et al, 2019;Hart et al, 2005;Yang et al, 2020).…”

“…Effects of forest fires on fungal communities have been reported from several chronosequence studies (Holden et al., 2013; Sun et al., 2015; Yang et al., 2020) that mainly focused on the long‐term development of communities after the disturbance. Variation in short‐term responses in fungal communities related to reliable measurements of fire severity and post‐fire logging and the underlying mechanisms remain to be investigated (Dahlberg et al., 2001; Holden et al., 2016; Reazin et al., 2016; Salo & Kouki, 2018).…”

Forest fire induces short‐term shifts in soil food webs with consequences for carbon cycling

“…bacteria, fungi, and archaea), which act as a trophic ‘basement’ for the entire soil community (Coleman et al ., 2004; Wang et al ., 2012). Ectomycorrhizal fungi have also been shown to respond to fire, although impacts depend on the time since fire, the type of fire and ecosystem and the method used to characterise them (Taudiere et al ., 2017; Yang et al ., 2020). Furthermore, effects of fire on soil biota can be long‐lasting, with fire‐induced reductions in the abundance and diversity of soil animals being detected for decades (Zaitsev et al ., 2016), especially of surface‐dwelling fauna that are unprotected from fire, those with limited dispersal ability and predatory groups that suffer from reduced food availability (Malmström, 2010; Gongalsky and Persson, 2013).…”