The Science

Nutrient constraints on high-latitude carbon cycling remains uncertain in land models, yet critical for 21st century prediction. This study shows that improving land models requires better representation of winter soil biogeochemical and plant processes. The commonly applied approach to represent competition for nutrients (called Relative Demand) is unable to represent these non-growing season dynamics.

The Impact

Land model representations of processes associated with tundra shrub expansion are uncertain, yet have large impacts on high-latitude carbon cycling. This study shows that plants acquire 5-50% of their annual nutrient demands during the non-growing season, and these interactions strongly impact shrub expansion predictions. Models must account for these dynamics to accurately predict 21st century carbon cycling.

Summary

Permafrost soils contain as much carbon as currently exists in the atmosphere, and these soils are vulnerable to releasing that carbon as the Earth warms. However, the net effect of climate change on the carbon balance of these ecosystems also depends on plant growth, which will likely be enhanced by warming. Current land models used for carbon cycle predictions remain uncertain, and a large part of this uncertainty stems from the role of plant nutrient constraints. Although it is widely recognized that plants continue to acquire nutrients well past when aboveground activity has ceased, most large-scale land models ignore this process.

In this paper researchers applied a well-tested (including at several NGEE-Arctic sites) mechanistic model to explore the role of non-growing season processes on vegetation dynamics and 21^st century carbon cycling. The team found that non-growing season nutrient uptake ranges between 5 and 50% of annual uptake, with large spatial variability and plant type dependence. This plant nutrient acquisition strongly enhances 21^st century shrub expansion, and thereby ecosystem carbon storage. This work highlights the importance of including non-growing season plant processes in large-scale land models, such as DOE’s ELM

Principal Investigator

William J. Riley
Lawrence Berkeley National Laboratory
wjriley@lbl.gov

Program Manager

Daniel Stover
U.S. Department of Energy, Biological and Environmental Research (SC-33)
Environmental System Science
daniel.stover@science.doe.gov

Funding

This research was supported by Lawrence Berkeley National Laboratory as part of the Next Generation Ecosystems Experiments Arctic (NGEE–Arctic) project (DE-AC02-05CH11231). NGEE–Arctic is funded by the Office of Biological and Environmental Research (BER) in the U.S. Department of Energy’s (DOE) Office of Science.

References