Synthesis of a C-13-labeled tracer for stream DOC: Labeling tulip poplar carbon with (CO2)-C-13

摘要

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 13 C 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 (CO2)-C-13 to assess the distribution and level of C-13 enrichment in the tree tissues. In 2001, seedlings were grown with 25 times more (CO2)-C-13 to generate tissues with a C-13 signal strong enough for a C-13-DOC stream tracer addition. C-13 enrichment in the trees varied in each year and by tissue age and type. Tissues formed during labeling (new) were more enriched in C-13 than tissues established prior to the (CO2)-C-13 injection (old). Stems were most enriched in C-13 in both new and old tissues. A higher percentage of (CO2)-C-13 was incorporated into seedlings in 2000 (59% +/- 1) than 2001 (43% +/- 0). Percent C-13 incorporation among tree tissue types paralleled biomass distributions. Although tree C and C-13 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 (CO2)-C-13 and had both humic and polysaccharide components. Results from a whole-stream C-13-DOC tracer addition demonstrated that tree C could be sufficiently labeled with (CO2)-C-13 to create a stream DOC isotope tracer with some polymeric constituents.