Wildfire severity reduces richness and alters composition of soil fungal communities in boreal forests of western Canada

Abstract

Wildfire is the dominant disturbance in boreal forests and fire activity is increasing in these regions. Soil fungal communities are important for plant growth and nutrient cycling postfire but there is little understanding of how fires impact fungal communities across landscapes, fire severity gradients, and stand types in boreal forests. Understanding relationships between fungal community composition, particularly mycorrhizas, and understory plant composition is therefore important in predicting how future fire regimes may affect vegetation. We used an extreme wildfire event in boreal forests of Canada's Northwest Territories to test drivers of fungal communities and assess relationships with plant communities. We sampled soils from 39 plots 1 year after fire and 8 unburned plots. High‐throughput sequencing (MiSeq, ITS) revealed 2,034 fungal operational taxonomic units. We found soil pH and fire severity (proportion soil organic layer combusted), and interactions between these drivers were important for fungal community structure (composition, richness, diversity, functional groups). Where fire severity was low, samples with low pH had higher total fungal, mycorrhizal, and saprotroph richness compared to where severity was high. Increased fire severity caused declines in richness of total fungi, mycorrhizas, and saprotrophs, and declines in diversity of total fungi and mycorrhizas. The importance of stand age (a surrogate for fire return interval) for fungal composition suggests we could detect long‐term successional patterns even after fire. Mycorrhizal and plant community composition, richness, and diversity were weakly but significantly correlated. These weak relationships and the distribution of fungi across plots suggest that the underlying driver of fungal community structure is pH, which is modified by fire severity. This study shows the importance of edaphic factors in determining fungal community structure at large scales, but suggests these patterns are mediated by interactions between fire and forest stand composition.

Estimation of Fungal Diversity and Identification of Major Abiotic Drivers Influencing Fungal Richness and Communities in Northern Temperate and Boreal Quebec Forests

“…Season should not have an impact on the global biodiversity retrieved. Unknown OTUs also represented a large proportion of the fungal diversity in our study, which was comparable to other studies using similar high-throughput sequencing methodologies [11,17,67,68]. Despite all the progress in fungal DNA barcoding, most of the fungal species in the world remains unknown for many reasons.…”

“…In our data, the genus Russula and Lactarius represented 84% of the OTUs from the Russulales (Table S3). Helotiales are common and frequently associated with roots in boreal forest [11,54], whereas the Agaricales are known to associate with bryophytes a dominant component of the boreal forest understory [58]. Agaricales and Russulales are also known to be abundant and diverse in temperate forests [59][60][61][62][63], which represented 32% of sites included in our study.…”

“…The three most frequent orders that characterized our regions were the Agaricales, Helotiales, and Russulales (Figure 2). These three groups are generally dominant in boreal forest [11,[53][54][55]. The genus Lactarius and Russula, from the order Russulales, are abundant and diverse ectomycorrhizal fungi in northern forests, especially because there are host generalists [14,56,57].…”

“…In our data, the genus Russula and Lactarius represented 84% of the OTUs from the Russulales (Table S3). Helotiales are common and frequently associated with roots in boreal forest [11,54], whereas the…”

“…In addition some species, especially edibles, are an important source of income and a significant component of the diet, particularly in developing countries and remote regions [10]. Unfortunately, fungal diversity can change because of time, climate, biota, topography, natural disturbance, or human caused perturbation and contamination [11][12][13][14]. For these reasons, there is interest in developing approaches to predict various facets of fungal diversity, and how it is likely to change over space and time in natural and managed ecosystems.…”