13C labeling of plant assimilates using a simple canopy-scale open air system

A simple system based on web-FACE technology was designed and implemented as an approach to label plant-assimilated carbon (C) with 13C. The labeling system avoids the use of a chamber or other enclosure, instead distributing CO2 heavily enriched in 13C at near atmospheric concentrations to the tree foliage through the use of porous tubing. The system was applied to three plantation grown juvenile larch (Larix spp.) trees during the daylight hours over the course of five days in the middle of the growing season. Relative to control trees, fumigation with enriched CO2 resulted in significantly 13C-enriched foliar respiration and nighttime soil respiration. Enrichment was also created in the foliar tissue, but differences between labeled and control trees were not statistically significant. Temporal and spatial variation in the strength of the isotopic label did occur, and modifications to the system are suggested to limit the variation. The approach should enable the implementation of pulse-chase experiments designed to understand plant source-sink relationships or experiments designed to understand the flux of C from plant roots into the soil food web.