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 C-13 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 C-13 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 C-13 over time, and their composition signature of C-13 were analyzed by the isotope ratio mass spectrometer technique. Results We found a significantly greater decline in assimilated C-13 of shoot and living root for the heavily grazed swards compared to other stocking rates, with the highest relocation rate of C-13 into soil C pool compared to other fractions. In addition, light grazing significantly allocated C-13 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.

Automated summary

This study aimed to evaluate the carbon allocations between the above- and belowground components of a grassland ecosystem in response to changes of stocking rate. Results showed a significantly greater decline in assimilated C-13 for heavily grazed swards compared to other stocking rates, indicating the highest relocation rate of C-13 into soil C pool. Light grazing, on the other hand, significantly allocated C-13 assimilates in the belowground pool, especially in live root and topsoil C-pools.