Peat decomposability in managed organic soils in relation to land use, organic matter composition and temperature
Organic soils comprise a large yet fragile carbon (C) store in the global C cycle. Drainage, necessary for agriculture and forestry, triggers rapid decomposition of soil organic matter (SOM), typically increasing in the order forest < grassland < cropland. However, there is also la...
| Main Authors: | , , , |
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| Format: | Article |
| Language: | English |
| Published: |
Copernicus Publications
2018-02-01
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| Series: | Biogeosciences |
| Online Access: | https://www.biogeosciences.net/15/703/2018/bg-15-703-2018.pdf |
| Summary: | Organic soils comprise a large yet fragile carbon (C) store in the global C
cycle. Drainage, necessary for agriculture and forestry, triggers rapid
decomposition of soil organic matter (SOM), typically increasing in the order
forest < grassland < cropland. However, there is also
large variation in decomposition due to differences in hydrological
conditions, climate and specific management. Here we studied the role of SOM
composition on peat decomposability in a variety of differently managed
drained organic soils. We collected a total of 560 samples from 21 organic
cropland, grassland and forest soils in Switzerland, monitored their CO<sub>2</sub>
emission rates in lab incubation experiments over 6 months at two
temperatures (10 and 20 °C) and related them to various soil
characteristics, including bulk density, pH, soil organic carbon (SOC)
content and elemental ratios (C / N, H / C and O / C). CO<sub>2</sub>
release ranged from 6 to 195 mg CO<sub>2</sub>-C g<sup>−1</sup> SOC at 10 °C
and from 12 to 423 mg g<sup>−1</sup> at 20 °C. This variation occurring
under controlled conditions suggests that besides soil water regime, weather
and management, SOM composition may be an underestimated factor that
determines CO<sub>2</sub> fluxes measured in field experiments. However,
correlations between the investigated chemical SOM characteristics and
CO<sub>2</sub> emissions were weak. The latter also did not show a dependence on
land-use type, although peat under forest was decomposed the least. High
CO<sub>2</sub> emissions in some topsoils were probably related to the accrual of
labile crop residues. A comparison with published CO<sub>2</sub> rates from
incubated mineral soils indicated no difference in SOM decomposability
between these soil classes, suggesting that accumulation of recent, labile
plant materials that presumably account for most of the evolved CO<sub>2</sub> is
not systematically different between mineral and organic soils. In our data
set, temperature sensitivity of decomposition (Q<sub>10</sub> on average
2.57 ± 0.05) was the same for all land uses but lowest below 60 cm in
croplands and grasslands. This, in turn, indicates a relative accumulation of
recalcitrant peat in topsoils. |
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| ISSN: | 1726-4170 1726-4189 |