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

[摘要] The Tibetan Plateau has a significant role with regard to atmospheric circulation and the monsoonin particular. Changes between a closed plant cover and open bare soil are one of the strikingeffects of land use degradation observed with unsustainable range management or climate change,but experiments investigating changes of surface properties and processestogether with atmospheric feedbacksare rare and have not been undertaken in the world's two largest alpine ecosystems, the alpinesteppe and the Kobresia pygmaea pastures of the Tibetan Plateau. Weconnected measurementsof micro-lysimeter, chamber, ¹³C labelling, and eddy covariance and combined theobservations with land surface and atmospheric models, adapted to the highland conditions. Thisallowed us to analyse how three degradation stages affect the water and carbon cycle of pastureson the landscape scale within the core region of the Kobresia pygmaea ecosystem. Thestudy revealed that increasing degradation of the Kobresia turf affects carbon allocationand strongly reduces the carbon uptake, compromising the function of Kobresia pastures asa carbon sink. Pasture degradation leads to a shift from transpiration to evaporation while a change in the sum ofevapotranspiration over a longer period cannot be confirmed. The results show an earlier onset ofconvection and cloud generation, likely triggered by a shift inevapotranspiration timing when dominated by evaporation. Consequently,precipitation starts earlier and clouds decrease the incoming solar radiation. In summary, thechanges in surface properties by pasture degradation found on the highland have a significantinfluence on larger scales.

[学科分类] 地球化学与岩石