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| Titel |
Utilisation of young and old soil carbon sources by microbial groups differ during the growing season and between experimental treatments in a long-term field experiment |
| VerfasserIn |
Gunnar Börjesson, Lorenzo Menichetti, Barry Thornton, Colin Campbell, Thomas Kätterer |
| Konferenz |
EGU General Assembly 2014
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 16 (2014) |
| Datensatznummer |
250094421
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| Publikation (Nr.) |
 EGU/EGU2014-9829.pdf |
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| Zusammenfassung |
| Soil organic matter (SOM)is the largest active carbon pool in the terrestrial environment.
SOM is a key factor for soil fertility, but is also important for the sequestration of atmospheric
CO2. In agricultural soils, management of plant residues and the use of organic fertilisers
play important roles for maintaining SOM. Switching from C3 plants to C4 plants such as
maize, enables a natural labelling in situ; when coupled with compound specific 13C isotope
analysis of phospholipid fatty acids (PLFAs) it allows the proportion of new C (fixed after the
switch added to soil from above- and belowground litter and root exudates) and the
proportion of old C (fixed prior to the switch derived from turnover of organic matter)
utilised by the soil microbial community to be determined. (new paragraph) A field
experiment in Sweden, amended with different mineral and organic fertilisers since
1956, was grown with C3 plants, mainly cereals until 1999. From the year 2000
silage maize was grown every year. In 2012, soil from four replicate plots of five
experimental treatments, N fertilised, N fertilised amended with straw and sewage
sludge, and two controls (bare fallow and cropped unfertilised) were sampled three
times, at the start, middle and end of the growing season. Phospholipid fatty acids
(PLFAs) were extracted from all soil samples and analysed for concentrations and
13C content. (new paragraph) Total PLFA concentrations and also the PLFA/SOM
ratios increased with SOM in the different treatments. Seasonal variation in total
PLFA was small except for the most SOM-rich treatment (sewage sludge) where
concentrations significantly decreased during the growing season indicating the
depletion of a labile SOM pool. Weighted mean values of δ13C in PLFAs show that the
plots fertilised with only calcium nitrate had the highest δ13C-values in PLFAs
before (-20.24 o) and after the vegetation period (-20.37 o), due to a large input of
13C-enriched plant material. However, during the vegetation period the values were
much lower (-21.85 o). This coincided with a strong increase of the PLFA 18:2
(from 0.99 up to 2.37 nmol g dry wt soil-1), indicating utilisation of old organic
matter by fungi, while mono-unsaturated PLFAs, indicating Gram-negative bacteria,
were more frequent before and after the growing season. Microbial dynamics in
the unfertilised control followed the same seasonal pattern but PLFAs were less
enriched in 13C due to lower yields compared with the N-fertilised treatment. The
addition of organic amendments (straw or sewage sludge) lowered δ13C-values in
PLFAs below values of the control due to input of labile material with C3-origin.
PLFAs in the bare fallow treatment, that had not received plant carbon inputs during
twelve years, were most 13C depleted among the treatments but still enriched by
about 2o compared with SOM, indicating a degree of microbial fractionation. |
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