Measuring ecosystem CO 2 emission sources in a northern hardwood forest Laura Brodman Larson 1 , Claire Phillips 2 , Karis McFarlane 2 Monitor respired CO 2 and 14 CO 2 at nested spatial scales. Acknowledgements: This material is based upon work supported by the S.D. Bechtel, Jr. Foundation and by the National Science Foundation under Grant No. 0952013 and Grant No. 0934931 (East Bay Noyce Fellows only) and Grant No. 0833353 (check funding spreadsheet if needed). Any opinions, findings, and conclusions or recommendations expressed in this material are those of the authors and do not necessarily reflect the views of the S.D. Bechtel, Jr. Foundation or the National Science Foundation. This project has also been made possible with support of the National Marine Sanctuary Foundation. The STAR program is administered by the Cal Poly Center for Excellence in Science and Mathematics Education (CESaME) on behalf of the California State University (CSU). This work is performed under the auspices of the U.S. Department of Energy by Lawrence Livermore National Laboratory under Contract DE-AC52-07NA27344. LLNL-POST-567312 Grant No. 0952013 0934931 Subsurface sampling (4 pits, including a trenched pit, x 7 levels) allow us to partition soil CO 2 production by depth. Flask air samples of 14 CO 2 collected at 45feet in the air at Willow Creek AmeriFlux site in Wisconsin Tree trunk samples of 14 CO 2 collected using respiration chamber attached to trees. Soil CO 2 has more bomb- C than the present atmosphere suggesting the carbon is years to decades old. Respired CO 2 is about 50- 50 root respiration and organic matter decomposition. 14 CO 2 was similar throughout the profile. Deep in the soil, respired CO 2 was much younger than solid bulk soil. Impacts of soil on canopy 14 CO 2 not (yet) detected. 360 370 380 390 400 410 25 30 35 40 45 50 55 60 CO2 ppm  14 C Aug 15 Aug 24 Sept 10 Sept 23 Oct 24 Currently measuring canopy 14 CO 2 profiles to characterize possible soil influences. 1. Syringe was used to create a vacuum 2. A pre-evacuated collection tube was used to collect CO 2 3. Stainless steel tube and fitting to connect collection tube to tree 4. Valve to allow CO 2 to enter vial  CO 2 produced in soils appears to be older than current photosynthesis. This CO 2 contains 30‰ more 14 C than the atmosphere.  Tree trunk CO 2 were also slightly older than current photosynthesis.  We found no clear evidence of bomb carbon from soil or tree trunk respiration in whole-ecosystem respired 14CO 2 ; however, additional data and method improvements for atmospheric sampling are forthcoming.  Future research may include more measurements of respired CO 2 from tree trunks, including a larger variety of species. Forests represent an important carbon sink that partially offsets rising levels of atmospheric CO 2 (Goodale et al., 2002). However, carbon that is stored in forest trees and soil is vulnerable t0 loss, and could potentially return to the atmosphere through respiration. We investigated the age of respired CO 2 to determine whether forest respiration contains older carbon from soils and trees, or is composed of “young” recently-photosynthesized carbon. Using radiocarbon (14C) measurements we assessed the age of CO2 respired from soils, tree trunks, and the whole forest canopy, to see whether any of these sources emitted older, stored carbon. Research Questions: 1) How old is CO 2 respired from soil?? 2) Do tree trunks respire recently-fixed carbon, or older “bomb” carbon from reserves? 3) Can “bomb” carbon from soils or tree trunks be detected in canopy CO 2 ? Canopy 14C was highly variable, and there was no obvious contributions of bomb- C from soil or trees. 1 2 3 4 1 Walter T. Helms Middle School 2 Lawrence Livermore National Laboratory San Pablo, CA Livermore, CA cams.llnl.gov CO 2 was converted to solid carbon (graphite). By using extremely high temperatures in the presence of hydrogen and an iron catalyst, the CO 2 is reduced to graphite. The graphite is then sent through the Accelerator Mass Spectrometer to determine the carbon isotope ratio. CO2 -300 -200 -100 0 100 Del 14C Depth (cm) -60 -40 -20 0 Bulk soil CO2 Roots CO2 SOM CO2 Air 9/12/11 CO2 Air 10/26/11 CO2 Air 3/26/12 http://cams.llnl.gov We sampled tree trunk CO 2 based on methods by Muhr et al (2011)and Ubierna et al (2009). Species Common Name Specimen D 14 C (‰) Acer saccharum Marsh. Sugar maple 1 28.0 ± 4.6 Acer saccharum Marsh. Sugar maple 2 43.9 ± 6.7 Acer saccharum Marsh. Sugar maple 3 36.9 ± 5.3 Tilia americana L. Basswood 1 41.9 ± 5.5 Fraxinus americana L. White ash 1 56.6 ± 8.2 Tree trunk emissions had amounts of 14C intermediate between soil respiration and the background atmosphere. Respiration from tree stems may be a source of bomb-C to the atmosphere. References Goodale, C. et al., Forest Carbon Sinks in the Northern Hemisphere. Ecological Applications, 2002,12(3), 891–899 by the Ecological Society of America. Muhr, J. et al., Radiocarbon in tree stem CO2 efflux: CO2 emitted by trees is older than expected. Poster session presented at: 44 th Annual American Geological Union Fall Meeting; 2011 December 5‐9; San Francisco, CA. Ubierna, N. et al., A new method to measure carbon isotope composition of CO2 respired by trees: stem CO2 equilibration. Functional Ecology, 2009, 23, 1050–1058 doi: 10.1111/j.1365‐2435.2009.01593.