Periodic Reporting for period 1 - PERMTHAW (Permafrost thaw – decadal responses to climate change)
Période du rapport: 2016-05-01 au 2018-04-30
This project aims to understand the future that lies ahead, following thaw and establishment of new non-permafrost ecosystems, and how the predicted climate variability will influence these soils on a decadal timescale. By using a natural occurring permafrost degradation transects, this project investigates how the C and N cycling changes following thaw. Moreover, by using laboratory incubation the project provided unique insights in how these cycles will respond to the changing climate long after the formation of ‘new’ ecosystems, giving a decadal perspective on permafrost thaw.
The investigated natural permafrost thaw gradient used in this study provided contrasting result compared to the heavily investigated carbon-rich emission hotspots usually highlighted in climate change discussion. Our result indicated that with increased vegetation and change towards a shrub-dominated landscape these mineral-based soils significantly reduces the methane emission due to a reduction in the anaerobic environment in the surface soil and an increase in methane consumption in this part of the soil. Furthermore, the long-term decomposition of carbon in the deeper former permafrost soils remains at a low emission rate, attributing most of the C and N cycling to the surface layer where even the carbon sequestration balance the decomposition rates from the deeper soils.
The in situ observations also revealed striking evidence of a change in methane dynamics with a reduction in methane emission and even a pronounced consumption of atmospheric methane following the transition to post permafrost shrub-dominated ecosystems. These changes in fluxes were confirmed by a microbial scanning of the soils where an increase of the methane-consuming methanotrophs was evident in surface soils following also with time after the final thaw. Similar a decrease in the abundance of methane-producing methanogens was evidenced in deeper soil layers. Furthermore, a pronounced seasonality of was observed among the methanotrophs indicating that several strands are active with different optima in environmental conditions as pH, soil moisture and temperature.
The decomposition rates and temperature sensitivity of the deeper, former permafrost, soils indicate a rapid release of carbon at the initial incubation decreasing to a slower decomposition. This is in line with several earlier studies, but the release of carbon from these soils is profoundly lower than the previous report that highlights the carbon-rich systems of Siberia and Northern Canada/Alaska. Our results are more in line with the up to 87% of the Arctic that can be characterized as mineral soils providing a new view of the permafrost dynamics in the Arctic region.
The results from the PERMTHAW project is currently under preparation for two major publications to be submitted during 2019, with additional one already submitted manuscript and two upcoming once based on additional data generated from the project.