The influence of environmental, soil carbon, root, and stand characteristics on soil CO 2 efflux in loblolly pine ( Pinus taeda L.) plantations located on the South Carolina Coastal Plain

Abstract

While the effect of soil temperature and moisture on soil CO 2 efflux ( E c) has been widely investigated, the relationship between E c and soil carbon (C), root, and stand parameters has not been comprehensively examined or quantified across extensive spatial and temporal scales. We measured E c in loblolly pine ( Pinus taeda L.) stands located on the South Carolina Coastal Plain across sites, seasons, and ages. Concurrent with E c 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 E c. Using linear regression analysis, we determined that E c was most highly correlated with soil temperature alone ( R 2=0.263). Mineral soil [C] alone explained a small, but significant amount of E c 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 E c. Other variables tested were not significantly correlated with E c. 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 E c 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 E c and stand age.