The temporal and spatial response of soil fungal community composition and potential function to wildfire in a permafrost region in Canada

The permafrost regions of the boreal forest store a large amount of carbon, which can be affected by ecological disturbance, especially the interference of forest fires. Understanding the dynamic responses of the post-fire soil fungal community is essential for predicting soil carbon dynamics. We used a post-fire chronosequence (areas with 3, 25, 46 and >100 years post fire [ypf]) in Canadian boreal forests with continuous permafrost to examine the responses of fungal communities and fungal genes associated with biogeochemical cycling to fire in the surface and near-surface permafrost layers (0-5, 5-10 and 10-30 cm depth). We hypothesized that as the forest recovers from fire, the fungal communities and functional genes associated with biogeochemical cycling will also recover temporally and spatially, which will in turn affect soil carbon storage. Our results demonstrate that the fire has long-term effects on fungal communities and functions in the surface and near-surface soils. The fungal species richness in the 0-5 and 5-10 cm soil layers increased with time since fire, which required at least 46 years to recover to pre-fire levels. Ascomycota in each of the soil layers in the recently burned area (3 ypf) and ericoid mycorrhizas Oidiodendron maius in the 10-30 cm soil layer in the control area were recognized as indicator taxa. The examination of functional genes revealed that the diversity of potential genes and the expression of genes related to carbon degradation (e.g. chitinase, cellobiase, exoglucanase and endoglucanase) in recently burned area increased in the surface soil, whereas, decreased in the deep soil, suggesting the fire affect the loss of carbon differently in the surface and deep soils in the early stages after fire. In conclusion, the fires significantly altered the fungal communities and functional genes related to carbon storage along the soil vertical gradients and along the post-fire chronosequence. Read the free Plain Language Summary for this article on the Journal blog.