Wiegner, T.N., L.A. Kaplan, J.D. Newbold, and P.H. Ostrom. 2005. Ecosystems 8:501–511.
Ecosystem tracer-level additions would benefit from a stable isotope-labeled source of complex organic molecules. We tested a method to label tree C with 13C and create a stable isotope tracer for stream dissolved organic carbon (DOC) using tulip poplar (Liriodendron tulipifera L.) seedlings. In 2000, seedlings were grown with 0.82 moles of 13CO2 to assess the distribution and level of 13C enrichment in the tree tissues. In 2001, seedlings were grown with 25 times more 13CO2 to generate tissues with a 13C signal strong enough for a 13C-DOC stream tracer addition. 13C enrichment in the trees varied in each year and by tissue age and type. Tissues formed during labeling (new) were more enriched in 13C than tissues established prior to the 13CO2 injection (old). Stems were most enriched in 13C in both new and old tissues. A higher percentage of 13CO2was incorporated into seedlings in 2000 (59% ±1) than 2001 (43% ±0). Percent 13C incorporation among tree tissue types paralleled biomass distributions. Although tree C and 13C were equally soluble in both years, a greater percentage of tree C went into solution in 2001 (30%) than 2000 (20%). The water-soluble tree C accounted for approximately 12% of the injected 13CO2 and had both humic and polysaccharide components. Results from a whole-stream 13C-DOC tracer addition demonstrated that tree C could be sufficiently labeled with 13CO2 to create a stream DOC isotope tracer with some polymeric constituents.
NSF Award No. DEB-0096276. Title: LTREB: Stream ecosystem structure and function within a maturing deciduous forest. Duration: August 1998–July 2003. Principal Investigator: L. A. Kaplan. Co-principal investigators: B. W. Sweeney, T. L. Bott, J. D. Newbold, J.K. Jackson, and L. J. Standley.