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

Yue-mei Zhang, Zhao-lei Qu, Outi-Maaria Sietiö, Xuan Zhou, Jussi Heinonsalo, Kajar Köster, Frank Berninger, Jukka Pumpanen, Hui Sun

This is a plain language summary of a Functional Ecology research article which can be found here.

The permafrost regions of boreal forests store a large amount of carbon, which can be affected by ecological disturbances, especially from forest fires. Soil microbes, especially fungi, play an important role in the carbon cycle by affecting the decomposition of organic matter. Understanding the dynamic responses of the soil fungal community post-fire is essential for predicting soil carbon dynamics.

In this study, we used a post-fire chronosequence (areas with 3, 25, 46 and > 100 years post fire) in Canadian boreal forests with continuous permafrost. We examined the responses to fire of fungal communities and fungal genes associated with biogeochemical cycling in the surface and near-surface permafrost layers (0-5, 5-10 and 10-30 cm depth). We found that fire has long-term effects on fungal communities and functions in surface and near-surface soils. Fungal species richness in the 0-5 and 5-10 cm soil layers increased with time since fire, and required at least 46 years to recover to pre-fire levels. The diversity of potential genes and the genes associated with carbon degradation in the 0-5 cm soil layer increased in the recently burned area, suggesting an increased loss of carbon storage in surface soils in the early stages after fire. In contrast, those genes associated with carbon degradation in the 10-30 cm soil layer decreased, indicating that fire suppressed the loss of carbon storage in deeper soils.

The four post-fire areas in a permafrost region in Canada. (a) >100 years post-fire, (b) 46 years post-fire, (c) 25 years post-fire, and (d) 3 years post-fire (credit: Kajar Koster)

In summary, fire significantly altered the fungal communities and functional genes related to the carbon cycle along the soil vertical gradients and along the post-fire chronosequence. Our results demonstrate that fire changes the fungal communities and functional genes in surface and near-surface soils in boreal forests, which may affect carbon storage in permafrost regions. To better understand the effects of natural disturbances on forests, it is necessary to construct a framework to study the specific role of the soil microbiome in post-fire forest recovery and nutrient cycling.

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