Root Nonstructural Carbohydrates and Their Relationship with Autotrophic Respiration of Loblolly Pine (Pinus taeda L.)

Abstract

Separating soil respiration (R_s) into heterotrophic (R_H) and autotrophic (R_A) components often relies on root-severing techniques with the presumption that R_A 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. R_S and R_A declined asymptotically, reduced by 86 and 95 percent, respectively. Correlation coefficients between R_A 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 R_S, and the steady decline in R_S and R_A over time, validates the use of field-installed root-severing cores to measure R_H.

Keywords:

• Autotrophic respiration
• carbon fluxes
• forest ecosystems
• nonstructural carbohydrates
• soil respiration

Additional information

Funding

This research was supported by the Pine Integrated Network: Education, Mitigation, and Adaptation Project (PINEMAP), a Coordinated Agricultural Project funded by the US Department of Agriculture (USDA) National Institute of Food and Agriculture (NIFA), Award No. 2011-68002-30185. Additional support was provided by the Virginia Agricultural Experiment Station and the McIntire-Stennis Program of the USDA NIFA.