Distinctions in carbon partitioning of a montane pasture and a grazing exclosure plot on the Tibetan Plateau revealed by 13CO2 pulse labeling
2 Institut für Bodenkunde, Universität Hannover
3 Fachbereich Geographie, Universität Marburg
P 1.16 in Ecosystem Function
Since 1959 settle programs change the grazing activity on the Tibetan Plateau. Near the villages grazing pressure increases leading to land degradation. The opposite effect is visible in remote areas where grazing pressure decreases and thus leads to changes in vegetation pattern. In the latter tall grasses become more abundant. To clarify the effect of land use changes on carbon (C) cycle on the Tibetan Plateau it is necessary to characterize the distinctions in belowground C allocation of both grazed and ungrazed grassland to ascertain if the system either functions as C source or sink.
In situ 13CO2 pulse labeling was accomplished on 1) a montane Kobresia-Stellera chamaejasme grassland that is used as winter pasture for yaks, and 2) on a grazing exclosure plot simulating decreasing grazing pressure where large grazers are excluded since 2002, both on the Qinghai-Tibetan Plateau in 3400 m.a.s.l. The average partitioning pattern of assimilated C was chased during 27 days from July 27 until August 22, 2009.
At the grazed plots almost 50 ± 11% of net assimilated C is used for shoot growth and 35 ± 3% is translocated belowground of which 20 ± 3% is recovered in soil respiration. In contrast, on the ungrazed plots only 30 ± 9% is used for shoot growth and 13 ± 2% is transferred belowground of which 7 ± 1% is recovered in soil respiration. Only 1% of net assimilated C is used for root growth in both grazed and ungrazed plots. Losses due to shoot respiration are twice as high in the ungrazed as in the grazed version.