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| Titel |
Intensive soil organic carbon losses by degradation of alpine Kobresia pasture on the Tibetan Plateau |
| VerfasserIn |
Per-Marten Schleuss, Felix Heitkamp, Elke Seeber, Sandra Spielvogel, Georg Miehe, Georg Guggenberger, Yakov Kuzyakov |
| Konferenz |
EGU General Assembly 2015
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 17 (2015) |
| Datensatznummer |
250109259
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| Publikation (Nr.) |
 EGU/EGU2015-9152.pdf |
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| Zusammenfassung |
| Kobresia grasslands of the Tibetan Plateau cover an area of ca. 450,000 km2. They are of
high global and regional importance as they store large amounts of carbon (C) and
nitrogen (N) and provide food for grazing animals. However, intensive grassland
degradation in recent decades destroyed mainly the upper root-mat/soil horizon. This has
dramatic consequences for SOC storage against the background of climate change and
further grazing pressure. We investigated the impact of pasture degradation on SOC
storage and hypothesized that SOC stocks strongly decreased due to a reduction of
C-input by roots as consequence of vegetation cover loss by overgrazing, SOM
decomposition and soil erosion. We selected a sequence of six degradation stages
(DS1-6).
As initial trigger of grassland degradation, the high grazing pressure reduces the ability of
Kobresia pastures to recover from disturbances (e.g. by freezing and drying events,
herbivory, trampling). Once the root mats are destroyed, the occurring root-mat
cracks increase due to soil erosion, SOC decomposition and trampling activities of
livestock.
The SOC stocks and contents decreased along the degradation sequence from intact to
highly disturbed stages. Carbon stocks declined from intact Kobresia root mats
(DS1) to bare soil patches (DS6) by about 70%. The thickness of the upper soil
horizons strongly declined from DS1 to DS6. Considering the bare soil patches
(DS6) on average 10 cm of the most fertile topsoil were removed. This clearly
suggests that soil erosion strongly contributed to SOC losses, especially from topsoil
with highest SOC contents. A strong decrease of the vegetation cover (mainly K.
pygmaea) demonstrated that soil degradation also resulted in die-back of K. pygmaea.
Consequently, root biomass decreased along the degradation sequence (DS1-2 >
DS3-4 > DS5-6), indicating lower belowground C input from roots. We found
decreasing δ13C values with increasing degradation stages within the upper 20 cm of
soil. Higher δ13C values were found for intact root mats (DS1), whereas lowest
δ13C signatures occurred for the highly degraded stages (DS5-6). This observation
seems to be unusual, because δ13C values are supposed to increase with increasing
decomposition. However, the δ13C signatures agreed well with lignin contents,
which increased along the degradation sequence. Since lignin is 13C depleted, the
δ13C shift clearly indicates SOM decomposition and relative enrichment of lignin
components. Using root biomass as indicator for C- input and δ13C values for SOM
decomposition, we could explain 70% of decreasing SOC contents using a multiple linear
regression model. We conclude that grassland and soil degradation led to large
SOC loss due an absence of root C-input, SOM decomposition and soil erosion. |
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