Kirschbaum, M.U.F.
(1995). The temperature dependence of soil organic matter
decomposition and the effect of global warming on soil organic carbon storage.
Soil Biology & Biochemistry 27: 753-760.
One of the key
questions in climate change research relates to the future dynamics of the
large amount of C that is currently stored in soil organic matter. Will the
amount of C in this pool increase or decrease with global warming? The future
trend in amounts of soil organic C will depend on the relative temperature
sensitivities of net primary productivity and soil organic matter decomposition
rate. Equations for the temperature dependence of net primary productivity have
been widely used, but the temperature dependence of decomposition rate is less
clear.
The literature was
surveyed to obtain the temperature dependencies of soil respiration and N
dynamics reported in different studies. Only laboratory-based measurements were
used to avoid confounding effects with differences in litter input rates,
litter quality, soil moisture or other environmental factors. A considerable
range of values has been reported, with the greatest relative sensitivity of
decomposition processes to temperature having been observed at low
temperatures.
A relationship fitted
to the literature data indicated that the rate of decomposition increases with
temperature at 0°C with a Q10 of almost 8. The temperature
sensitivity of organic matter decomposition decreases with increasing temperature,
indicated by the Q10 decreasing with temperature to be about
4.5 at 10°C and 2.5 at 20°C. At low temperatures, the temperature sensitivity
of decomposition was consequently much greater than the temperature sensitivity
of net primary productivity, whereas the temperature sensitivities became more
similar at higher temperatures. The much higher temperature sensitivity of
decomposition than for net primary productivity has important implications for
the store of soil organic C in the soil.
The data suggest that
a 1°C increase in temperature could ultimately lead to a loss of over 10% of
soil organic C in regions of the world with an annual mean temperature of 5°C,
whereas the same temperature increase would lead to a loss of only 3% of soil
organic C for a soil at 30°C. These differences are even greater in absolute
amounts as cooler soils contain greater amounts of soil organic C. This
analysis supports the conclusion of previous studies which indicated that soil
organic C contents may decrease greatly with global warming and thereby provide
a positive feed-back in the global C cycle.