Effects of permafrost thaw on the global nitrogen cycle: the role of thermokarst systems

Global change leads modifications in climate on Arctic regions, where temperatures have risen faster than in any other region on
Earth. Those regions store vast amounts of soil organic matter (SOM) in permafrost soils, covering ~25% of terrestrial surface. When
they thaw, it leads to rapid release of nutrients and greenhouse gases (GHG). So far, many studies have addressed the importance of
permafrost thaw and carbon cycle. However, little attention has been paid to the nitrogen (N) cycle, despite nitrous oxide (N2O) is a
powerful GHG, an ozone-depleting agent and may create an unaccounted permafrost-climate feedback. If permafrost contains large
amounts of ice, thaw occurs abruptly leading to ground surface collapse and new ecosystems (ponds, lakes) formation. This process
is called thermokarst and covers wide areas of the northern permafrost region (up to 40%). Thermokarst impacts ecology and
biogeochemistry by enhancing microbial activity, which together with seasonal thaw, may release nutrients and GHGs. Despite its
importance, the impact of permafrost thaw on global N cycle still remains understudied, and almost unknown in thermokarst
systems. For this reason, climate scenarios must include the effect of SOM degradation and seasonal thaw on the microbial
communities responsible for N cycling. NITROKARST will address the contribution of thermokarst systems to the global N cycle and
N2O budget, looking at those microbial pathways able to promote the transformation of N compounds and how thawing controls
the operation and intensity of these processes. For this purpose, N cycling will be studied along a thermokarst transect by combining
isotope tracing, multi-omics and microcosm incubations. This multidisciplinary approach will increase our knowledge about the fate
of N in thermokarst-affected permafrost soils and provide climate scenarios which consider microbial N cycling and metabolism
changes under different states of thaw.