Carbon pools and fluxes in a Tibetan alpine Kobresia pygmaea pasture partitioned by coupled eddy-covariance measurements and 13CO2 pulse labeling

More than a century of Grain for Green Program is expected to restore soil carbon stock on alpine grassland revealed by field 13 C pulse labeling

“…Roots can be considered the primary source of C in the surface soil (Kumar et al, 2006) because more than two thirds of the roots are in the 0-5 cm soil layer (Table 1). Our findings agree with those from recent studies of an alpine Kobresia meadow on the QTP Ingrisch et al, 2015). While the results were similar for the roots in a nearby Kobresia meadow, the vertical distribution of the soil m E ( 13 C) was different, as only 9.1-13.9% of the 13 C recovery in the soil was in the top 5 cm .…”

“…Although there were significant differences in the m E ( 13 C) in the C pools of both grasslands, partitioning of photoassimilate (% of recovered 13 C) in the plant-soil system 25 days after labeling was similar to that from various other previous studies (Hafner et al, 2012;Ingrisch et al, 2015;Kuzyakov, 2001;Street et al, 2013;Wu et al, 2010;Zou et al, 2014). Percentage of recovered 13 C in the shoots in this study (35.75-38.11%) was similar to that reported by Hafner et al (2012) (38.5-42.5%) and Wu et al (2010) (28.9%), but was greater than the 8.14-19.6% reported by Gao et al (2015); Ingrisch et al (2015), and Zou et al (2014).…”

“…The biexponential decay model, described as the sum of two exponential functions, was fitted to the decline of the shoots, soil CO 2 efflux and ecosystem m E ( 13 C). Ingrisch et al (2015) used a similar method to describe the contribution of 13 C to the decline in the CO 2 efflux and estimated the MRTs and TRs of belowground C. This provides TRs for two metabolic stages. The first stage represents respiration and a rapid use of photoassimilate by plants, reallocation to belowground, and rhizodeposits by microorganisms, while the second slow stage represents partitioning to storage, structural growth and defense compounds, use of transformation products, and dying shoots and roots.…”

“…The 13 C pulse labeling made it possible to explore the fate of newly assimilated C, including its partitioning within plants and to the soil, its storage within ecosystems and losses into the atmosphere in the natural and GfGP grasslands under in situ conditions (Gao et al, 2015;Hafner et al, 2012;Ingrisch et al, 2015;Street et al, 2013;Wu et al, 2010;Zhao et al, 2015;Zou et al, 2014). The results indicated that, although the 13 CO 2 uptake rate was greater in the GfGP grassland than in the natural grassland (Figs.…”

“…13 C pulse labeling can be used to explore the SOC sequestration rate, i.e., newly assimilated C partitioned into SOC, under in situ conditions (Gao et al, 2015;Hafner et al, 2012;Ingrisch et al, 2015;Street et al, 2013;Wu et al, 2010;Zhao et al, 2015;Zou et al, 2014). Using the method from Street et al (2013) that is based on the robust positive linear relationship between gross primary productivity (GPP) and annual net primary productivity (ANPP) reported by Litton et al (2007), the product of GPP and % of recovered 13 C in the soil provides estimates of the SOC sequestration rate and total photosynthesized C partitioned into the soil (Litton et al, 2007;Roper et al, 2013;Street et al, 2013).…”