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A free-air system for long-term stable carbon isotope labeling of adult forest trees
Citation:
Grams, T. E., H. Werner, D. Kuptz, W. Ritter, F. Fleischmann, C. P. ANDERSEN, AND R. Matyssek. A free-air system for long-term stable carbon isotope labeling of adult forest trees. TREES. Springer, New York, NY, 25:187-198, (2011).
Impact/Purpose:
Stable carbon isotopes, in particular when employed in labeling experiments, are an ideal tool to broaden our understanding of carbon dynamics of forest ecosystems.
Description:
Stable carbon (C) isotopes, in particular employed in labeling experiments, are an ideal tool to broaden our understanding of C dynamics in trees and forest ecosystems. Here, we present a free-air exposure system, named isoFACE, designed for long-term stable C isotope labeling in the canopy of 25 m tall forest trees. Labeling of canopy air was achieved by continuous release of CO2 with a δ13C of −46.9‰. To this end, micro-porous tubes were suspended at c. 1 m distance vertically through the canopy, minimizing CO2 gradients from the exterior to the interior and allowing for C labeling exposure during periods of low wind speed. Target for CO2 concentration ([CO2]) increase was ambient +100 μmol mol−1. Canopy [CO2] stayed within 10% of the target during more than 57% of the time and resulted in a drop of δ13C in canopy air by 7.8‰. After 19 labeling days about 50% of C in phloem sugars and stem CO2 efflux were turned over and 20–30% in coarse root CO2 efflux and soil CO2. The isoFACE system successfully altered δ13C of canopy air for studying turn-over of C pools in forest trees and soils, highlighting their slow turn-over rates.
