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]