Future nitrogen availability has major impact on the fate of carbon sequestration in Northern Eurasia
Boreal forests in Northern Eurasia store vast amounts of carbon and play a major role in the planet’s carbon cycle, but that role is strongly impacted by human activities.
Northern Eurasia plays a significant role in the planet’s carbon cycle as it includes roughly 70% of the Earth’s boreal forests and more than two-thirds of the Earth’s permafrost, the perennially frozen ground found in cold climates that holds substantial amounts of carbon. The availability of soil inorganic nitrogen is a critical controller of plant productivity and carbon sequestration in the forests of Northern Eurasia. However, nitrogen availability in forests has been altered by human activities, such as the enhanced atmospheric nitrogen deposition from fossil fuel combustion and ammonia emissions from the application of nitrogen fertilizers to croplands, the release of nitrogen from the decomposition of organic matter on abandoned agricultural land (both fertilized and unfertilized), and the release of nitrogen from the decomposition of organic matter exposed by climate change-induced permafrost degradation. Understanding the future availability of nitrogen and its effect on carbon sequestration in Northern Eurasia is key to developing more effective regional and sub-regional strategies for addressing global change (climate and land-use change) impacts.
In a new study published last Tuesday in Nature Communications, researchers from the Marine Biological Laboratory, the University of California, Davis, MIT and Purdue University explore how changes in nitrogen availability associated with permafrost degradation, atmospheric nitrogen deposition, and the abandonment of agricultural land to forest regrowth influence carbon storage in the region’s forest vegetation over the 21st century. They use a process-based terrestrial ecosystem model that represents carbon-nitrogen interactions under two different scenarios of global change. They find that enhanced nitrogen availability from these factors increases carbon sequestration in forest vegetation and accounts for 30-50% of the future net carbon sinks estimated for Northern Eurasia. They further find that under a high warming and timber forest harvesting scenario, enhanced nitrogen availability increases carbon storage in trees by 13.4 Pg C, mainly caused by permafrost degradation. Meanwhile, under a low warming and forest regrowth scenario, achieved by climate mitigation and forest restoration efforts, enhanced nitrogen availability increases tree carbon storage of 27.8 Pg C or double that under the large warming scenario. In that case, the main driver is the abandonment of agricultural land to forest regrowth. They also find complex patterns in how the distribution of land carbon sources and sinks across the region evolve over time, highlighting the complex regional dynamics among climate change, land-use change and the carbon cycle.
This study provides new insight into the role of human activity on future nitrogen availability and its influence on carbon sequestration in Northern Eurasia forests. This study further highlights the importance of accounting for carbon-nitrogen interactions when assessing the regional and sub-regional impacts of climate and land-use change policies.