Soil 13 CO2 Signatures to Investigate Root Dynamics in a Loblolly Pine (Pinus taeda L.) and Switchgrass (Panicum Virgatum L.] Intercropped Bioenergy System.

Loblolly pine [Pinus taeda L.] and switchgrass [Panicum virgatum L.] intercropped systems may be a useful management strategy for growing biofuels, livestock forage, erosion control, and wildlife habitat. Understanding competitive interactions belowground are necessary in order to manage these more complex systems properly. In this study located near Dover, NC on Atlantic Coastal Plain, loblolly pine and switchgrass are being grown together with loblolly pine planted on beds 20 feet (6.09 meters) apart and switchgrass grown in the interbed area. Due to the different photosynthetic pathways of the two species, we propose to use the unique d13C signatures of soil CO2 as a surrogate for the presence and relative abundance of loblolly pine and switchgrass roots. Gas wells, made from 1 inch diameter PVC pipe and sealed with a silicon septum, were installed in transects from the pine bed to the center of the row with 2.5 feet (76.2 cm) between each of 5 wells, for each depth of 15, 30, 45, and 60cm in 4 plots ( 5 transects * 4 depths = 20 wells per plot). We hypothesize that unique 13C-CO2 signatures will be found with depth and distance from beds and that the roots of pine and switchgrass will be occupying relatively different areas of the soil profile. Specifically switchgrass roots will dominate the upper portion of the soil profile, especially as distance from the pine bed increases, after switchgrass senescence pine roots will occupy more of the upper portion of the soil profile.