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

Descrizione del progetto

L’importanza dei suoli di permafrost colpiti da termocarsismo nel ciclo globale dell’azoto

I cambiamenti globali stanno modificando il clima delle regioni artiche, dove le temperature aumentano più velocemente che in qualsiasi altra parte della Terra. Queste regioni immagazzinano grandi quantità di sostanza organica del suolo nei terreni permafrost, che rilasciano rapidamente nutrienti e gas serra quando si scongelano. Lo scongelamento dà luogo a processi di termocarsismo che si verificano bruscamente, portando al collasso della superficie del suolo e allo sviluppo di ecosistemi (stagni e laghi) dove gli ambienti anaerobici favoriscono l’attività microbica. Con il riscaldamento dell’Artico, lo scioglimento del permafrost e i processi di termocarsismo aumenteranno, rilasciando azoto solubile nell’ambiente e favorendo così la decomposizione microbica della sostanza organica del suolo. Il progetto NITROKARST, finanziato dall’UE, approfondirà i meccanismi alla base del ciclo dell’azoto nei sistemi termocarsici, esaminando il modo in cui i percorsi microbici promuovono la trasformazione dell’azoto e come il disgelo controlla il funzionamento di questi processi.

Obiettivo

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 in the 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.

Permafrost with low ice content suffers a gradual top-down thawing process during seasonal freeze-thaw period. However, thaw of ice-rich permafrost results in thermokarst processes, which occur abruptly and lead to ground surface collapse. Its widespread occurrence affects large areas (~40% of the northern permafrost region) contributing to develop ecosystems like ponds and lakes. In such ecosystems, the presence of anaerobic environments enhances microbial activity. As Arctic warms, permafrost thaw and thermokarst processes will increase, releasing soluble N into the environment and enhancing microbial decomposition of SOM.

Hence, mineralization, nitrification and denitrification rates are expected to increase, and thus, N2O emissions to the atmosphere. Unfortunately, the impact of permafrost thaw on N cycling remains understudied, and almost unknown in thermokarst systems.
NITROKARST will explore the underlying mechanisms of the N cycle in thermokarst systems, looking at how microbial pathways promote N transformation and how thawing controls the operation of these processes. N cycling will be studied along a thermokarst transect by combining isotope tracing, metagenomics and microcosm incubations. This multidisciplinary approach will increase our knowledge about the importance of thermokarst-affected permafrost soils in the global N cycle.