『Abstract
Forest clear-cutting followed by soil preparation means disturbance
for soil microorganisms and disruption of N and C cycles. We measured
fluxes of N2O and dissolved organic carbon
(DOC) in upland soil (podzol) and adjacent peat within a clear-cut
forest catchment. Both soil types behaved in a similar way, showing
net uptake of N2O in the first year after
the clear-cutting, and turning to net release in the second. The
N2O flux dynamics were similar to those of
N content in logging residues, as reported from a nearby site.
As organic matter is used in the food web of the decomposers,
we attempted to explain the dynamics of N2O
uptake and release by measuring the concurrent dynamics of the
low molecular weight (LMW) fraction and the aromaticity of DOC
in a soil solution. The labile and most readily available LMW
fractions of DOC were nearly absent in the year following the
clear-cutting, but rose after two years. The more refractory high
molecular weight (HMW) fraction of DOC decreased two years after
the clear-cutting. The first year's net uptake of N2O
could be accounted for by the growth of decomposer biomass in
the logging residues and detritus from the degenerating ground
vegetation, resulting in immobilization of nitrogen. Simultaneously,
the labile, LMW fraction of DOC became almost completely exhausted.
The low availability of the LMW fraction could retard the growth
and cause the accumulated decomposer biomass to collapse. During
the following winter and summer the fraction of LMW clearly increased,
followed by increased N2O emissions. The
presence of LMW DOC fractions, not the concentration of DOC, seems
to be an important controller for N2O liberation
after a major disturbance such as clear-cutting and site preparation.
The complex connection between DOC characteristics, nitrification
or denitrification merits further studies.
Keywords: Dissolved organic carbon; DOC; Nitrous oxide; N2O; Forestry; Clear-cutting』
Abbreviations
Introduction
Materials and methods
Study site
N2O and CH4 measurements
N measurements
Quantification and characterization of DOC
BOD
Statistical tests
Results
N2O and CH4
Water table and N leaching
Total DOC, its molecular size and aromaticity, and BOD
Vegetation cover
Discussion
Conclusions
Acknowledgments
References