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PI-Submitted Research Highlights for
Terrestrial Ecosystem Science Program

21st Century Tundra Shrubification Could Enhance Net Carbon Uptake of North America Arctic Tundra Under an RCP8.5 Climate Trajectory

William J. Riley

Highlight

24 May 2018

Tundra shrubification will offset respiratory carbon losses under RCP8.5.

The Science 
Scientists at Lawrence Berkeley National Laboratory (LBNL) and the Next-Generation Ecosystem Experiments (NGEE)–Arctic project applied an ecosystem model, ecosys, to examine the effects of North America Arctic tundra plant dynamics on ecosystem carbon balances from 1980 to 2100 under Representative Concentration Pathway (RCP) 8.5 scenario. Between 1982 and 2100 and averaged across the region, predicted increases in relative dominance of woody versus nonwoody plants increased ecosystem annual net primary productivity that offset concurrent increases in annual heterotrophic respiration, resulting in an increasing net carbon sink over the 21st century. However, modeled soil temperatures were predicted to increase more slowly than air temperatures, implying that higher gains versus losses of carbon may be a transient response and not sustainable under further soil warming beyond 2100.

The Impact
Although several tundra warming experiments provide valuable warming scenarios, the responses of these experiments were largely dependent on site conditions. Further, these experiments cannot fully represent the warming effects associated with relatively slower changes in species composition and abundance. Thus, this modeling analysis allows researchers to extend beyond results from short-term warming experiments, which cannot characterize effects associated with decadal-scale changes in plant communities.

Summary
NGEE-Arctic scientists applied a mechanistic trait-based model (ecosys) that represents key biological, physical, and chemical processes controlling long-term carbon cycle dynamics. In particular, they examined the roles of plant internal resource allocation and remobilization and microbial soil carbon, nitrogen, and phosphorus transformations, along with soil thermal and hydrological dynamics, over the 21st century. The effects of projected increases in tundra shrub growth on net ecosystem productivity were shown to enhance the ecosystem carbon sink due to increasing woody vs. non-woody carbon stocks. The modeled gains in non-woody plant net primary productivity offset ecosystem respiration resulting in the tundra remaining a carbon sink through 2100.

Contacts
BER Program Manager
Daniel Stover
Terrestrial Ecosystem Science, SC-23.1
Daniel.Stover@science.doe.gov

Principal Investigator
William J. Riley
Lawrence Berkeley National Laboratory
Berkeley, CA 94720
wjriley@lbl.gov

Funding
This research was supported by the Office of Biological and Environmental Research (BER), within the U.S. Department of Energy Office of Science, under Contract No. DE-AC02-05CH11231 as part of the Next-Generation Ecosystem Experiments (NGEE)–Arctic project.

Publications
Mekonnen, A.M., W.J. Riley, and R.F. Grant. "21st century tundra shrubification could enhance net carbon uptake of North America Arctic tundra under an RCP8.5 climate trajectory." Environmental Research Letters 13(5), 054029 (2018). [DOI:10.1088/1748-9326/aabf28]

LBNL NGEE-Arctic

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