Auswirkung von Weidedegradation auf die Zusammensetzung und Funktion mikrobieller Gemeinschaften in Böden des Tibetischen Plateaus

Das Tibetische Plateau, mit seinen Kobresia pygmea Weiden, stellt eine globale Senke für organischen Kohlenstoff (OC) dar. Überweidung führt zur Zerstörung der Kobresia Wurzelmatten und damit zur Graslanddegradation. Dies hat massive OC Verluste und die Destabilisierung des Ökosystems zur Folge. Diese Arbeit analysiert den Effekt der degradationsbedingten veränderten Zusammensetzung der organischen Bodensubstanz (SOM) auf die Zusammensetzung der mikrobiellen Gemeinschaft und deren Funktion entlang einer Sequenz von sechs Degradationsstufen. Dazu wurden die Aktivitäten von sechs extrazellulären Enzyme gemessen sowie die Zusammensetzung der bakteriellen und pilzlichen Gemeinschaft (mittels t-RFLP Analyse gefolgt von Illumina MiSeq Sequenzierung) analysiert. So konnte die Zusammensetzung der mikrobiellen Gemeinschaft mit den vertikalen Gradienten der δ13C und δ15N-Werte, sowie den Neutralzucker-, Cutin-, Suberin- und Ligningehalten in Beziehung gesetzt werden. Mit zunehmender Degradation deuten negativere δ13C-Werte auf eine relative Anreicherung an 13C-armen Makromolekülen wie bspw. Lignin hin. Zusammen mit ebenfalls verringerten δ15N-Werten und veränderten C/N-Verhältnissen belegt dies einen verstärkten SOM-Abbau. Gleichzeitig nimmt die Aktivität von hydrolytischen Enzymen, mit fortschreitender Degradation zu. Lediglich in der letzten Degradationsstufe ist ein drastischer Rückgang der Aktivität dieser Enzymgruppe zu beobachten. Im Gegensatz dazu zeigen Phenoloxidasen (Mineralisation komplexer SOM) zunehmende Aktivitäten mit steigender Degradation die mit einer Anreicherung dieser Substrate (z.B. Ligin) einhergeht. Die beobachteten Änderungen der Enzymaktivitäten sind mit einer veränderten Zusammensetzung der mikrobiellen Gemeinschaft, besonders des Unterbodens, begleitet. So nehmen Actinobacteria mit der Degradation ab während Nitrosomonas zunehmenden, was einen steigenden Verlust von mineralisiertem N aus dem Boden erklärt. Bis jetzt ist unklar ob die degradationsbedingten funktionellen und strukturellen Veränderungen der mikrobiellen Gemeinschaft der Kobresia Grasländer reversibel sind, oder ob mit steigendem Verlust an Nährstoffen und Boden ein Punkt erreicht wird, der eine Erholung der Kobresia-Matten nicht mehr erlaubt

Pasture degradation modifies the water and carbon cycles of the Tibetan highlands

© Author(s) 2014. The Tibetan Plateau has a significant role with regard to atmospheric circulation and the monsoon in particular. Changes between a closed plant cover and open bare soil are one of the striking effects of land use degradation observed with unsustainable range management or climate change, but experiments investigating changes of surface properties and processes together with atmospheric feedbacks are rare and have not been undertaken in the world's two largest alpine ecosystems, the alpine steppe and the Kobresia pygmaea pastures of the Tibetan Plateau. We connected measurements of micro-lysimeter, chamber, 13C labelling, and eddy covariance and combined the observations with land surface and atmospheric models, adapted to the highland conditions. This allowed us to analyse how three degradation stages affect the water and carbon cycle of pastures on the landscape scale within the core region of the Kobresia pygmaea ecosystem. The study revealed that increasing degradation of the Kobresia turf affects carbon allocation and strongly reduces the carbon uptake, compromising the function of Kobresia pastures as a carbon sink. Pasture degradation leads to a shift from transpiration to evaporation while a change in the sum of evapotranspiration over a longer period cannot be confirmed. The results show an earlier onset of convection and cloud generation, likely triggered by a shift in evapotranspiration timing when dominated by evaporation. Consequently, precipitation starts earlier and clouds decrease the incoming solar radiation. In summary, the changes in surface properties by pasture degradation found on the highland have a significant influence on larger scales

Pasture degradation modifies the water and carbon cycles of the Tibetan highlands

© Author(s) 2014. The Tibetan Plateau has a significant role with regard to atmospheric circulation and the monsoon in particular. Changes between a closed plant cover and open bare soil are one of the striking effects of land use degradation observed with unsustainable range management or climate change, but experiments investigating changes of surface properties and processes together with atmospheric feedbacks are rare and have not been undertaken in the world's two largest alpine ecosystems, the alpine steppe and the Kobresia pygmaea pastures of the Tibetan Plateau. We connected measurements of micro-lysimeter, chamber, 13C labelling, and eddy covariance and combined the observations with land surface and atmospheric models, adapted to the highland conditions. This allowed us to analyse how three degradation stages affect the water and carbon cycle of pastures on the landscape scale within the core region of the Kobresia pygmaea ecosystem. The study revealed that increasing degradation of the Kobresia turf affects carbon allocation and strongly reduces the carbon uptake, compromising the function of Kobresia pastures as a carbon sink. Pasture degradation leads to a shift from transpiration to evaporation while a change in the sum of evapotranspiration over a longer period cannot be confirmed. The results show an earlier onset of convection and cloud generation, likely triggered by a shift in evapotranspiration timing when dominated by evaporation. Consequently, precipitation starts earlier and clouds decrease the incoming solar radiation. In summary, the changes in surface properties by pasture degradation found on the highland have a significant influence on larger scales

Pasture degradation modifies the water and carbon cycles of the Tibetan highlands

© Author(s) 2014. The Tibetan Plateau has a significant role with regard to atmospheric circulation and the monsoon in particular. Changes between a closed plant cover and open bare soil are one of the striking effects of land use degradation observed with unsustainable range management or climate change, but experiments investigating changes of surface properties and processes together with atmospheric feedbacks are rare and have not been undertaken in the world's two largest alpine ecosystems, the alpine steppe and the Kobresia pygmaea pastures of the Tibetan Plateau. We connected measurements of micro-lysimeter, chamber, 13C labelling, and eddy covariance and combined the observations with land surface and atmospheric models, adapted to the highland conditions. This allowed us to analyse how three degradation stages affect the water and carbon cycle of pastures on the landscape scale within the core region of the Kobresia pygmaea ecosystem. The study revealed that increasing degradation of the Kobresia turf affects carbon allocation and strongly reduces the carbon uptake, compromising the function of Kobresia pastures as a carbon sink. Pasture degradation leads to a shift from transpiration to evaporation while a change in the sum of evapotranspiration over a longer period cannot be confirmed. The results show an earlier onset of convection and cloud generation, likely triggered by a shift in evapotranspiration timing when dominated by evaporation. Consequently, precipitation starts earlier and clouds decrease the incoming solar radiation. In summary, the changes in surface properties by pasture degradation found on the highland have a significant influence on larger scales

Pasture degradation modifies the water and carbon cycles of the Tibetan highlands

© Author(s) 2014. The Tibetan Plateau has a significant role with regard to atmospheric circulation and the monsoon in particular. Changes between a closed plant cover and open bare soil are one of the striking effects of land use degradation observed with unsustainable range management or climate change, but experiments investigating changes of surface properties and processes together with atmospheric feedbacks are rare and have not been undertaken in the world's two largest alpine ecosystems, the alpine steppe and the Kobresia pygmaea pastures of the Tibetan Plateau. We connected measurements of micro-lysimeter, chamber, 13C labelling, and eddy covariance and combined the observations with land surface and atmospheric models, adapted to the highland conditions. This allowed us to analyse how three degradation stages affect the water and carbon cycle of pastures on the landscape scale within the core region of the Kobresia pygmaea ecosystem. The study revealed that increasing degradation of the Kobresia turf affects carbon allocation and strongly reduces the carbon uptake, compromising the function of Kobresia pastures as a carbon sink. Pasture degradation leads to a shift from transpiration to evaporation while a change in the sum of evapotranspiration over a longer period cannot be confirmed. The results show an earlier onset of convection and cloud generation, likely triggered by a shift in evapotranspiration timing when dominated by evaporation. Consequently, precipitation starts earlier and clouds decrease the incoming solar radiation. In summary, the changes in surface properties by pasture degradation found on the highland have a significant influence on larger scales

Pasture degradation modifies the water and carbon cycles of the Tibetan highlands

The Tibetan Plateau has a significant role with regard to atmospheric circulation and the monsoon in particular. Changes between a closed plant cover and open bare soil are one of the striking effects of land use degradation observed with unsustainable range management or climate change, but experiments investigating changes of surface properties and processes together with atmospheric feedbacks are rare and have not been undertaken in the world's two largest alpine ecosystems, the alpine steppe and the Kobresia pygmaea pastures of the Tibetan Plateau. We connected measurements of micro-lysimeter, chamber, 13C labelling, and eddy covariance and combined the observations with land surface and atmospheric models, adapted to the highland conditions. This allowed us to analyse how three degradation stages affect the water and carbon cycle of pastures on the landscape scale within the core region of the Kobresia pygmaea ecosystem. The study revealed that increasing degradation of the Kobresia turf affects carbon allocation and strongly reduces the carbon uptake, compromising the function of Kobresia pastures as a carbon sink. Pasture degradation leads to a shift from transpiration to evaporation while a change in the sum of evapotranspiration over a longer period cannot be confirmed. The results show an earlier onset of convection and cloud generation, likely triggered by a shift in evapotranspiration timing when dominated by evaporation. Consequently, precipitation starts earlier and clouds decrease the incoming solar radiation. In summary, the changes in surface properties by pasture degradation found on the highland have a significant influence on larger scales