Stocking rate changed the magnitude of carbon sequestration and flow within the plant-soil system of a meadow steppe ecosystem.

Aims: Livestock grazing is one of the most common utilization methods and exerts a significant effect on the carbon allocations between the above- and belowground components of a grassland ecosystem. The major aim of this study were to evaluate the proportions of 13C allocation to various C pools of the plant-soil system of a meadow steppe ecosystem in response to changes of stocking rate. Methods: In situ stable 13C isotope pulse labeling was conducted in a long-term grazing experiment with 4 stocking rate. Plant materials and soil samples were taken at eight occasions (0, 3, 10, 18, 31, 56 and 100 days after labeling) to analyze the decline in 13C over time, and their composition signature of 13C were analyzed by the isotope ratio mass spectrometer technique. Results: We found a significantly greater decline in assimilated 13C of shoot and living root for the heavily grazed swards compared to other stocking rates, with the highest relocation rate of 13C into soil C pool compared to other fractions. In addition, light grazing significantly allocated 13C assimilates in the belowground pool compared to other stocking rates, especially in the live root and topsoil C-pools. Conclusions: In this study, the effects of grazing on the carbon transfers and stocks within the plant-soil system of the meadow steppe were highly grazing pressure dependent. Plant-soil system in light stocking rate presented the highest C utilization efficiency, however, plants allocated more C to soil C pools with heavily stocking rate. [ABSTRACT FROM AUTHOR]