Observations of 14CO2 in ecosystem respiration from a temperate deciduous forest in Northern Wisconsin. Issue 4 (14th April 2015)

• Record Type: Journal Article
• Authors: Phillips, Claire L.; McFarlane, Karis J.; LaFranchi, Brian; Desai, Ankur R.; Miller, John B.; Lehman, Scott J.
• Is Part Of: Journal of geophysical research. Volume 120:Issue 4(2015:Jun.)
• Page Start: 600
• Page End: 616
• Publication Date: 2015-04-14
• Subjects: Geobiology -- Periodicals; Biogeochemistry -- Periodicals; Biotic communities -- Periodicals; Geophysics -- Periodicals; 577.14
• DOI: 10.1002/2014JG002808
• Languages: English
• ISSNs: 2169-8953

Abstract

<abstract abstract-type="main"> <title>Abstract</title> <p>The <sup>14</sup>CO<sub>2</sub> composition of plant and soil respiration can be used to determine the residence time of photosynthetically fixed carbon before it is released back to the atmosphere. To estimate the residence time of actively cycled carbon in a temperate forest, we employed two approaches for estimating the Δ<sup>14</sup>CO<sub>2</sub> of ecosystem respiration (Δ<sup>14</sup>C‐<italic>R</italic><sub>eco</sub>) at the Willow Creek AmeriFlux site in Northern Wisconsin, USA. Our first approach was to construct nighttime Keeling plots from subcanopy profiles of Δ<sup>14</sup>CO<sub>2</sub> and CO<sub>2</sub>, providing estimates of Δ<sup>14</sup>C‐<italic>R</italic><sub>eco</sub> of 121.7‰ in June and 42.0‰ in August 2012. These measurements are likely dominated by soil fluxes due to proximity to the ground level. Our second approach utilized samples taken over 20 months within the forest canopy and from 396 m above ground level at the nearby LEF NOAA tall tower site (Park Falls, WI). In this canopy‐minus‐background approach we employed a mixing model described by Miller and Tans (2003) for estimating isotopic sources by subtracting time‐varying background conditions. For the period from May 2011 to December 2012 the estimated Δ<sup>14</sup>C‐<italic>R</italic><sub>eco</sub> using the Miller‐Tans model was 76.8‰. Together, these Δ<sup>14</sup>C‐<italic>R</italic><sub>eco</sub> values represent mean <italic>R</italic><sub>eco</sub> carbon ages of approximately 1–19 years. We also found that heterotrophic soil‐respired Δ <sup>14</sup>C at Willow Creek was 5–38‰ higher (i.e., 1–10 years older) than predicted by the Carnegie‐Ames‐Stanford Approach global biosphere carbon model for the 1 × 1 pixel nearest to the site. This study provides much needed observational constraints of ecosystem carbon residence times, which are a major source of uncertainty in terrestrial carbon cycle models.</p> </abstract>