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 ( Rs) 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 ( Rh) and Rs, 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 Rs from control collars was 3.3 micromol CO2 m(-2) s(-1). Root exclusion tubes decreased Rs, providing an estimate of Rh. Mean Rh 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 Rh was corrected for root decay. The corresponding ratio of Rh to Rs ranged from 66% to 82%, depending on the estimation method. This study provides an estimate of Rh in longleaf pine forests, and demonstrates the potential for deep root exclusion tubes to provide relatively rapid assessments ( i. e., similar to 40 days post- treatment) of Rh in similar forests. The range in Rh to Rs is comparable to other reports for similar temperate coniferous ecosystems.