The fungal contribution to the carbon cycle of Subarctic and Arctic permafrost areas

Climate change is causing the thawing of Artic permafrost, which stores twice the amount of carbon than the atmosphere. The thawing process leads to the collapse of the landscape and the formation of thaw ponds that receive this organic matter (OM) and thus are considered hotspots for the carbon cycle. Microorganisms are responsible for breaking down organic compounds, which results in greenhouse gases (GHG) emissions. A massive release of previously frozen OM could not only threat Artic ecosystems but accelerate climate change globally. Therefore, there is an urge to understand how this OM is processed by microbial communities in thaw ponds, to further evaluate the impacts of a thawing Arctic. While there is a lot of ongoing research on this topic, a group of microorganisms is largely understudied: the aquatic fungi. Despite their role as decomposers of the OM in soil, we barely know about what fungi can do in water. Here I present my postdoc project aims to study the functional potential and carbon cycling activity of aquatic fungal communities in Arctic thaw ponds. Water and sediment from the ponds will be analyzed and combined with metagenomic data, fully sequenced fungal isolates, dissolved OM quality data, single cell sequencing, carbon assimilation assays (DNA stable-isotope probing) and metatranscriptomics to: a) analyze the functional potential, in terms of carbon degradation, of aquatic fungi across a thaw gradient (from pristine to degraded sites Figure 1); and b) conduct an in-depth functional analysis of the fungal community from a Swedish permafrost site significantly impacted by thawing. The degraded sites concentrate more terrestrial (allochthonous) OM, whereas the pristine sites present higher proportions of autochthonous dissolved OM, derived from primary production. These changes in OM were tightly linked to the taxonomic diversity of fungal species, and we have hypothesized that the functional potential of genes involved in carbon compounds breakdown would also be highly correlated with the quality of the OM. However, results showed weaker correlations, and thus, indicate functional redundancy of the fungal communities. Our next step now is to evaluate the activity of these genes through metatranscriptomics and stable isotope experiments. This project will increase the understanding on the role of aquatic fungal communities in carbon cycling in thaw ponds, an important step to better estimate the impacts of climate change in permafrost areas.