Soil CO2 efflux in loblolly pine (Pinus taeda L.) plantations on the virginia Piedmond and South Carolina coastal plain over a rotation-length chronosequence
We measured soil surface CO2 efflux (Fx) in loblolly pine stands (Pinus taeda L.) located on the Virginia Piedmont (VA) and South Carolina Coastal Plain (SC) in efforts to assess the impact climate, productivity, and cultural practices have on Fs in the managed loblolly pine ecosystem. The effect of stand age on Fs was examined using a replicated chronosequence approach in which stands ranging from 1 to 25 years since planting were investigated. Soil CO2 efflux was measured on both VA and Sc sites for over a year using a closed dynamic system. Multiple linear regression was used to evaluate Fx correlates and examine the relationship between candidate explanatory variables and Fs. Soil temperature (top 10 cm) was the major correlate with Fs on both locations. We observed a positive age effect on Fs in Va stands and no relationship between age and Fs in SC stands. Annual soil C efflux declined with stand age in SC due to both reductions in soil temperatures as crown closure occurs and a diminishing heterotrophic C substrate pool. Annual estimated efflux ranges from 16.7 to 13.2 Mg C ha-1 for 1 and 20-year-old stands, respectively. In contrast, annual soil C efflux increased with age in VA stands as a result of the positive relationship between stand age anf Fsm which appears to be related to an increase in the contribution of root respiration to total Fs over time. In VA stands, efflux estimates range from 7.6 to 12.3 Mg C ha-1 for 1 and 20-year-old stands, respectively. These results demonstrate the need to further consider the impact forest management and within-region vvariabiliity have on soil C efflux over time when estimating C budgets.