U.S. Department of Energy Office of Biological and Environmental Research

PI-Submitted Research Highlights for
Terrestrial Ecosystem Science Program

The Whole-soil Carbon Flux in Response to Warming: Soils Could Release Much More Carbon Than Expected as Climate Warms

Margaret S. Torn
Lawrence Berkeley National Laboratory

Highlight

(A) Soil CO2 production increased by about 35% in the heated plots with 40% of the response coming from >15 cm and 10% from >30 cm. 

(B) Mean apparent Q10 over 20 months is similar at all depths (±SE, black diamonds).

March 15, 2017

Deeper soil layers more sensitive to warming than previously thought, Berkeley Lab scientists find

The Science
Berkeley Lab scientists created the first replicated field experiment to warm the whole profile of a mineral soil, in a conifer forest in California. Warming the whole profile by 4oC increased annual soil respiration by 34-37%. More than 40% of this increase in respiration came from below 15 cm depth, in other words below the depth considered by most studies.

The Impact
The impact of warming on soil CO2 flux is a major uncertainty in climate feedbacks. This whole-soil warming experiment found a larger respiration response than (1) many other controlled experiments, which may have missed the response of deeper soils, and (2) most models. Thus, currently the strength of the soil carbon-climate feedback may be underestimated.

Summary
Soil organic carbon harbors three times as much carbon as Earth’s atmosphere, more than half of that below 20 cm depth. The response of whole soil profiles to warming has not been tested in situ. In this deep warming experiment in mineral soil, CO2 production from all soil depths increased significantly with 4°C warming—annual soil respiration increased by 34-37%. All depths responded to warming with similar temperature sensitivities, driven by decomposition of decadal-aged carbon. Whole soil warming reveals a larger soil respiration response than many in situ experiments, most of which only warm the surface soil, and models.

In this year-round experiment, plots were warmed by a ring of 22 vertical heating cables installed to 2.4m depth. Three plots (3 m diameter each) were warmed and three served as controls. Soil respiration was measured three by chambers at the surface and gas tubes at 5 depths. Radiocarbon content of CO2 and soil fractions suggests that respiration—and its warming response—was dominated by decadal cycling carbon.

Contacts (BER PM)
Daniel Stover
SC-23.1
Daniel.Stover@science.doe.gov (301-903-0289)

PI Contact
Margaret S. Torn (co-Corresponding author)
Lawrence Berkeley National Laboratory
mstorn@lbl.gov
and
Caitlin Hicks Pries (first author)
Lawrence Berkeley National Laboratory
cehpries@lbl.gov

Funding
This material is based upon work supported by the U.S. Department of Energy, Office of Science, Office of Biological and Environmental Research, Terrestrial Ecosystem Science program under contract number DE-AC02-05CH11231.

Publication
Hicks Pries, C.E., C. Castanha, R.C. Porras, and M. S. Torn. The whole-soil carbon flux in response to warming. Science. Early Online Research March 9, 2017

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