CARBON KINETICS IN A BLACK CHERNOZEM WITH ROOTS IN-SITU

The rates of decomposition of roots and root-derived materials are nee ded 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 C-14 pulse-labeling and incubat ion methods. Plants were pulse-labeled (1 d) with (CO2)-C-14 25 d afte r emergence. Shoots were excised, and undisturbed soil cores containin g the roots of a single plant were incubated at 20 degrees C for 80 d. The experiment involved two barley cultivars, with six replications a t 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 barle y cultivars. The decemposition-rate constants for the resistant compon ents of the roots were also not significantly different between the tw o 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 co mponents. The average half life of C-14 in roots was 41 d for Abee and 71 d for Samson. The amount of root C-14 + soil C-14 under Samson was higher than under Abee during the incubation period. These results su pported our hypothesis that the cultivar that translocated more C-14-l abeled carbon into roots and root-derived material has greater microbi al respiration and greater C stabilization because a portion of added C remains in the soil after being transformed by microorganisms.