A PULSE-CHASE METHOD TO 13CARBON-LABEL DOUGLAS-FIR SEEDLINGS FOR DECOMPOSITION STUDIESMoore-Kucera, Jennifer1; Dick, Richard P.2Soil Science: January 2008 - Volume 173 - Issue 1 - pp 46-53 doi: 10.1097/ss.0b013e31815a665f Technical Articles Abstract Author Information Abstract Tracking litter decomposition and root carbon (C) flow via stable isotopes, such as 13C, is gaining popularity because of reliable and affordable mass spectrometry. Although model 13C-labeled compounds such as glucose or acetate are available commercially, there is a need for large quantities of 13C-labeled plant materials to realistically study decomposition, C cycling, and biogeochemical processes in situ or in the laboratory. The objective of this research was to determine whether a pulse-labeling technique to label Douglas-fir seedlings with 13CO2 would result in significant quantities of 13C-labeled needles, stems, and roots that would be sufficiently enriched for in situ tracking of plant C into soil organic matter fractions. Once a week, for up to 9 weeks, 670 Douglas-fir seedlings were exposed to 13CO2 in a closed chamber. The 13CO2 (99 at.%) was injected into the chamber in quantities proportional to the photosynthetic rate, providing about 3 L of 13CO2 in total. More than 1.5 kg of seedling dry matter was produced, and the 13C distribution was relatively similar among plant parts, with 1.57 in needles, 1.45 in stems, and 1.36 atom% 13C in roots compared with control litter that had less than 1.084 at.% 13C. Adding an additional pulse to one half the seedlings at 9 weeks resulted in needles and stems being further enriched over seedlings that had received 13CO2 pulses over 8 weeks. A 2-month field incubation study showed that for microcosms amended with labeled needle or root materials, 13C could be tracked into whole soil, free particulate organic matter, or the humin fraction (recalcitrant C pool that is insoluble in strong base or acid). The pulse-labeling technique and chamber design provide large quantities of 13C-labeled plant material that can be used to trace residue decomposition rates in field or laboratory studies. Author Information 1Department of Horticulture, Oregon State University, Corvallis, OR 97331. 2School of Environment and Natural Resources, Ohio State University, Columbus OH 43210-1085. Dr. Dick is corresponding author. E-mail: Richard.Dick@snr.osu.edu Received Sep. 12, 2006; accepted Aug. 29, 2007. © 2008 Lippincott Williams & Wilkins, Inc.