Abstracts |
Soil respiration is a combination of CO2 fluxes derived from a diversity of
belowground sources, many depending directly on the input of carbon from living plants. Here we
present data from two different forest ecosystems, a beech and a spruce forest, where a
partitioning of soil respiration was carried out. We used soil cores inside micro-pore meshes
together with periodic chamber-based measurements to estimate rhizosphere, mycorrhizal fungal and
microbial heterotrophic respiration. Calculated mycorrhizal mycelium respiration was 8% at the
spruce forest and 3% at the beech forest. Given the nature of the partitioning method these
values represent minimum estimates. The ratio of root-derived carbon respiration to heterotrophic
respiration was about 1:1 at both forest types. The relationship of each source with temperature
and photosynthesis, measured as gross primary productivity derived from eddy covariance
measurements, was subsequently explored. Both factors revealed effects specific to the
respiration source and the forest type. A response to temperature was evident in all cases except
for mycorrhizal mycelium respiration at the spruce forest (R-2 = 0.06, p = 0.41). Significant
correlations of photosynthesis with rhizosphere and mycorrhizal fungal respiration were found in
all cases. Peaks in correlation values showed time lags between photosynthetic activity and a
respiration response ranging from 1 day for the fungal component and 4 days for the rhizosphere
component at the beech forest(R-2 = 0.70, p < 0.01 and R-2 = 0.42, p < 0.05, respectively) to 5
days for both fluxes at the spruce forest (R-2 = 0.44, p < 0.01 and R-2 = 0.72, p < 0.01,
respectively). Results show that respiration of the mycorrhizal. Component cannot be predicted by
common temperature driven models in some ecosystems. They also indicate a strong influence of
forest canopy processes on the activity of roots and associated organisms. The specific response
in each vegetation type should be ideally explained by physiological mechanisms inherent to
different species as a next step towards understanding belowground carbon dynamics. (c) 2007
Elsevier B.V. All rights reserved.
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