『Abstract
To understand the rates of turnover of soil carbon, and hence
interactions between soil carbon pools and atmospheric CO2 levels, it is essential to be able to quantify
and characterize soil organic matter and mineral hosts for C.
Thermal analysis is uniquely suited to this task, as different
C compounds decompose during a heating cycle at different temperatures.
In ‘air’ (80％ He or N2, 20％ O2),
relatively labile cellulosic material decomposes between 300 and
350℃ and more refractory lignin and related materials decompose
between 400 and 650℃. Calcite and other common soil carbonate
minerals decompose at 750-900℃. Using thermal analysis connected
to a quadrupole mass spectrometer and to an isotope ratio mass
spectrometer, it is possible to simultaneously determine mass
loss during combustion, evolved gas molecular compositions, and
carbon isotope ratios for evolved CO2. as
an example of the potential of the technique, the evolution of
a fungally-degraded wheat straw shows initial isotopic heterogeneity
consistent with its plant origins (-23.8‰ v-PDB for cellulosic
material; -26.1‰ v-PDB for ligninic material), which homogenizes
at heavier δ13C values (-21.0‰ v-PDB) as lignin is
preferentially degraded by fungal growth. Simultaneously, it is
shown that the evolution of nitrogen compounds is initially dominated
by decomposition of aliphatic N within the cellulosic component,
but that with increasing fungal degradation it is the ligninic
component that contributes N to evolved gases, derived presumably
from pyrrolic and related N groups produced during soil degradation
through condensation reactions. Overall, the use of thermal analysis
coupled to quadrupole and stable isotope mass spectrometry appears
to have considerable potential for the characterization of discrete
carbon pools that are amenable to the modelling of carbon turnover
within soil systems.
Keywords: soil; organic matter; carbon turnover; thermal analysis;
carbon sequestration; carbon isotopes.』
Introduction
The analytical system
Thermal characteristics of soil organic matter
Stable isotope and chemical analysis of evolved gases
Further applications of TG-DSC-QMS-IRMS
Acknowledgements
References