Carbon transfer, partitioning and residence time in the plant-soil system: a comparison of two <sup>13</sup>CO<sub>2</sub> labelling techniques
Various <sup>13</sup>CO<sub>2</sub> labelling approaches exist to trace carbon (C) dynamics in plant-soil systems. However, it is not clear if the different approaches yield the same results. Moreover, there is no consistent way of data analysis to date. In this study we comp...
| Main Authors: | , , |
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| Format: | Article |
| Language: | English |
| Published: |
Copernicus Publications
2014-03-01
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| Series: | Biogeosciences |
| Online Access: | http://www.biogeosciences.net/11/1637/2014/bg-11-1637-2014.pdf |
| Summary: | Various <sup>13</sup>CO<sub>2</sub> labelling approaches exist to trace carbon (C)
dynamics in plant-soil systems. However, it is not clear if the different
approaches yield the same results. Moreover, there is no consistent way of
data analysis to date. In this study we compare with the same experimental
setup the two main techniques: pulse and continuous labelling. We evaluate
how these techniques perform to estimate the C transfer time, the C
partitioning along time and the C residence time in different plant-soil
compartments.
<br><br>
We used identical plant-soil systems (<i>Populus
deltoides</i> × <i>nigra</i>, Cambisol soil) to compare the pulse
labelling approach (exposure to 99 atom % <sup>13</sup>CO<sub>2</sub> for three
hours, traced for eight days) with a continuous labelling (exposure to
10 atom % <sup>13</sup>CO<sub>2</sub>, traced for 14 days). The experiments were
conducted in climate chambers under controlled environmental conditions.
Before label addition and at four successive sampling dates, the plant-soil
systems were destructively harvested, separated into leaves, petioles, stems,
cuttings, roots and soil and soil microbial biomass was extracted. The soil
CO<sub>2</sub> efflux was sampled throughout the experiment. To model the C
dynamics we used an exponential function to describe the <sup>13</sup>C signal
decline after pulse labelling. For the evaluation of the <sup>13</sup>C
distribution during the continuous labelling we applied a logistic function.
<br><br>
Pulse labelling is best suited to assess the minimum C transfer time from the
leaves to other compartments, while continuous labelling can be used to
estimate the mean transfer time through a compartment, including short-term
storage pools. The C partitioning between the plant-soil compartments
obtained was similar for both techniques, but the time of sampling had a
large effect: shortly after labelling the allocation into leaves was
overestimated and the soil <sup>13</sup>CO<sub>2</sub> efflux underestimated. The results
of belowground C partitioning were consistent for the two techniques only
after eight days of labelling, when the <sup>13</sup>C import and export was at
equilibrium. The C mean residence times estimated by the rate constant of the
exponential and logistic function were not valid here (non-steady state).
However, the duration of the accumulation phase (continuous labelling) could
be used to estimate the C residence time.
<br><br>
Pulse and continuous labelling techniques are both well suited to assess C
cycling. With pulse labelling, the dynamics of fresh assimilates can be
traced, whereas the continuous labelling gives a more integrated result of C
cycling, due to the homogeneous labelling of C pools and fluxes. The logistic
model applied here, has the potential to assess different parameters of C
cycling independent on the sampling date and with no disputable assumptions. |
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| ISSN: | 1726-4170 1726-4189 |