Abstract
Separating soil respiration (Rs) into heterotrophic (RH) and autotrophic (RA) components often relies on root-severing techniques with the presumption that RA will approach zero as root nonstructural carbohydrate (NSC) supply diminishes. To test this assumption, we evaluated changes in carbon dioxide (CO2) flux rates and NSC concentrations after severing Pinus taeda L. roots using laboratory and field approaches. After an 86-day laboratory incubation, soluble, insoluble, and total NSCs decreased by 60, 29, and 43 percent, respectively. RS and RA declined asymptotically, reduced by 86 and 95 percent, respectively. Correlation coefficients between RA and soluble, insoluble, and total NSCs were 0.90, 0.69, and 0.93, respectively. In a field study, respiration stabilized after 40 days with mean rates in root-severed areas 21. ± 0.5 percent less than in undisturbed areas. This relationship between total NSCs and RS, and the steady decline in RS and RA over time, validates the use of field-installed root-severing cores to measure RH.