The influence of environmental, soil carbon, root, and stand characteristics on soil CO2 efflux in loblolly pine (Pinus taeda L.) plantations located on the South Carolina Coastal Plain

While the effect of soil temperature and moisture on soil CO2 efflux (Ec) has been widely investigated, the relationship between Ec and soil carbon (C), root, and stand parameters has not been comprehensively examined or quantified across extensive spatial and temporal scales. We measured Ec in loblolly pine (Pinus taeda L.) stands located on the South Carolina Coastal Plain across sites, seasons, and ages. Concurrent with Ec measurements, we monitored soil temperature (top 10 cm) and soil moisture (top 10 cm) along with mineral soil C concentration [C], coarse woody debris (CWD), root surface area, and root volume in the top 20 cm of the mineral soil below the measurement chamber. We also examined the effects of stand age, stand volume, and site quality on Ec. Using linear regression analysis, we determined that Ec was most highly correlated with soil temperature alone (R^2=0.263). Mineral soil [C] alone explained a small, but significant amount of Ec variance (R^2=0.026). When all variables were considered simultaneously, only soil temperature (R^2=0.249), mineral soil C (R^2=0.0378), and root surface area (R^2=0.0149) explained a significant amount of variance in Ec. Other variables tested were not significantly correlated with Ec. Mineral soil C concentration was greater in samples taken directly adjacent to trees (on beds) compared with samples between rows (interbeds), which partially explained why we observed greater Ec rates next to trees. With increasing stand age, CWD decreased and root surface area increased suggesting that opposite shifts in total root and microbial respiration over time are responsible for the lack of correlation between Ec and stand age.