Partitioning longleaf pine soil respiration into its heterotrophic and autotrophic components through root exclusion

Rapid and accurate estimations of the heterotrophic and autotrophic components of total soil respiration (R_s) are important for calculating forest carbon budgets and for understanding carbon dynamics associated with natural and management-related disturbances. The objective of this study was to use deep (60 cm) root exclusion tubes and paired control (i.e., no root exclusion) collars to estimate heterotrophic respiration (R_h) and R_s, respectively, in three 26-year-old longleaf pine (Pinus palustris Mill.) stands in western Georgia. Root biomass was measured in root exclusion tubes and control collars after 102-104 days of incubation and fine root biomass loss from root exclusion was used to quantify root decay. Mean R_s from control collars was 3.3 micromol·CO₂·m^-2· s^-1. Root exclusion tubes decreased R_s, providing an estimate of R_h. Mean R_h was 2.7 micromol·CO₂·m^-2· s^-1 when uncorrected by pretreatment variation, root decay, or soil moisture compared to 2.1 micromol·CO₂·m^-2· s^-1 when R_h was corrected for root decay. The corresponding ratio of R_h to R_s ranged from 66% to 82%, depending on the estimation method. This study provides an estimate of R_h in longleaf pine forests, and demonstrates the potential for deep root exclusion tubes to provide relatively rapid assessments (i.e., ~40 days post-treatment) of R_h in similar forests. The range in R_h to R_s is comparable to other reports for similar temperate coniferous ecosystems.