Continuous 13C and 15N Labeling of Tree Litter using a Climate-Controlled Chamber

Substrates with a unique stable isotope signature provide researchers with the ability to trace nutrients through food webs. Plant material labeled with carbon (C-13) can be produced by exposure to carbon dioxide (CO2) with an isotopic composition that differs from ambient conditions during photosynthesis. Labeling can occur continuously or be repeated over several pulses. Each method has a high cost either in the form of expensive control systems or significant time investments. In 2012, we built a large growth chamber and used an inexpensive, open-source Arduino(TM) microcontroller to monitor and control interior conditions so that we could produce leaf litter dually enriched in C-13 and nitrogen (N-15) for future incubation experiments. We performed a labeling experiment on 73 saplings representing seven species in 2012 and repeated the labeling on 30 saplings of one species in 2013. We successfully produced over 1 kg of litter enriched in both isotopes; N-15-enrichment (N-15: 759.2 +/- 133.7 parts per thousand) was much greater than C-13 (C-13: 11.2 +/- 3.4 parts per thousand). Roots (161.0 +/- 8.6 parts per thousand) were much more enriched in C-13 than litter (11.2 +/- 3.4 parts per thousand), indicating significant translocation of newly fixed carbohydrates. Some species allocated more resources toward their leaves as trees with the most enriched litter had the least enriched roots. C-13 litter enrichment in 2012 was at the lower end of the range reported by similar studies; however, litter from trees labeled over two seasons achieved a higher level of enrichment (401.4 +/- 65.5 parts per thousand).