Carbon kinetics in a Black Chernozem with roots in situ

The rates of decomposition of roots and root-derived materials are needed to assess the contribution of these materials to sequestration of organic carbon in soil. The objective of this study was to examine the kinetics of different forms of C in a Black Chernozem, with roots in situ under two barley cultivars, using 14C pulse-labeling and incubation methods. Plants were pulse-labeled (1 d) with 14CO2 25 d after emergence. Shoots were excised, and undisturbed soil cores containing the roots of a single plant were incubated at 20 °C for 80 d. The experiment involved two barley cultivars, with six replications at six sampling dates (days 0, 5, 10, 25, 40 and 80). The percentage of the labile components in roots of Abee (48%) was greater than that of Samson (39%), but the half lives of the labile components (0.693 k−1) of the roots were not significantly different between the two barley cultivars. The decomposition-rate constants for the resistant components of the roots were also not significantly different between the two barley cultivars. This indicated that the difference between the two barley cultivars in root decomposition rate could be explained by the difference in the ratios of the labile components to the resistant components. The average half life of 14C in roots was 41 d for Abee and 71 d for Samson. The amount of root 14C + soil 14C under Samson was higher than under Abee during the incubation period. These results supported our hypothesis that the cultivar that translocated more 14C-labeled carbon into roots and root-derived material has greater microbial respiration and greater C stabilization because a portion of added C remains in the soil after being transformed by microorganisms. Key words: Carbon kinetics, carbon sequestration, roots in situ, 14C pulse-labeling, Black Chernozem