Soil CO2 efflux across four age classes of plantation loblolly pine (Pinus taeda L.) on the Virginia Piedmont

Soil CO2 efflux resulting from microbial and root respiration is a major component of the forest C cycle. In this investigation, we examined in detail how soil CO2 efflux differs both spatially and temporally with respect to stand age for loblolly pine (Pinus taeda L.) plantations on the Virginia Piedmont. Throughout a 12-month period, efflux rates were measured both near the base of trees and midway between planting rows in stands of four age classes. Mean soil CO2 efflux rates measured during the 12-month study were 1.72, 2.58, 2.84, and 2.90 (mu)mol/m^2/s for 1- to 2-year-old, 4- to 6-year-old, 8- to 12-year-old, and 20- to 25-year-old stands, respectively. Time series analysis revealed that stand age had a significant effect on soil CO2 efflux rate. Additionally, mean efflux rates were consistently higher near the tree and time series analysis revealed that measurement position had a significant effect on soil CO2 efflux rate. Mean soil CO2 efflux rates, by position, for the 12month study were 2.72 and 2.28 (mu)mol/m^2/s for the near and away measurement positions, respectively. Regression analysis was used to examine the influence of soil and climatic factors on seasonal changes in soil CO2 efflux. The most influential factors affecting soil CO2 efflux during the 12-month study were soil temperature, soil moisture, stand age, and measurement position. We believe respiring roots significantly influence soil CO2 efflux of plantation loblolly pine and account for differences observed between stands of different ages as well as spatial differences observed within a given stand.