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Biogeosciences Discuss., 7, 1603-1631, 2010
www.biogeosciences-discuss.net/7/1603/2010/ doi:10.5194/bgd-7-1603-2010 © Author(s) 2010. This work is distributed under the Creative Commons Attribution 3.0 License. |
Technical Note: A combined soil/canopy chamber system for tracing δ13C in soil respiration after a 13CO2 canopy pulse labelling
1ETH Zürich, Institute of Plant, Animal and Agroecosystem Sciences, Universitätsstraße 2, 8092 Zürich, Switzerland
2Georg-August-Universtät Göttingen, Chair of Bioclimatology, Büsgenweg 2, 37077 Göttingen, Germany
Abstract. In this study we present a combined soil/canopy chamber system that allows the investigation of carbon flow through the atmosphere-plant-soil system via a 13CO2 canopy labelling approach – especially when using short vegetation such as tree saplings. The developed chamber system clearly separates soil and canopy compartment in order to (a) prevent physical diffusion of 13C tracer into the soil chamber during a 13CO2 canopy pulse labelling (b) study stable isotope processes in soil and canopy individually and independently. In combination with novel laser spectrometry, measuring CO2 (Aerodyne Research Inc.) and H2O (Los Gatos Research Inc.) isotopologue mixing ratios at a rate of 1 Hz, we were able to trace the label transport from leaves to roots in small beech saplings (Fagus sylvatica L.) without interference due to contamination of the soil matrix and/or canopy re-labelling via tracer returning from soil respiration. A very tight coupling between above- (photosynthesis) and belowground (soil respiration) processes was found, where newly assimilated carbon fixed from the 13CO2 atmosphere re-appeared in soil respiration 2 h after it has been photosynthetically fixed. We were able to demonstrate that leaf metabolism acts on substrate for soil respiration on a diurnal timescale, with input of fresh photosynthates during daytime and starch re-mobilisation during nighttime. Long-term fluctuations in the δ13C of soil respiration, as observed under reduced water availability, could not be described by any biological or instrumental mechanism, as they did occur in an atypical ca. 15 hourly rhythm – potential mechanisms driving these fluctuations are hypothesized.
Citation: Barthel, M., Sturm, P., Gentsch, L., and Knohl, A.: Technical Note: A combined soil/canopy chamber system for tracing δ13C in soil respiration after a 13CO2 canopy pulse labelling, Biogeosciences Discuss., 7, 1603-1631, doi:10.5194/bgd-7-1603-2010, 2010.