Root length and biomass in mixtures of broomsedge with loblolly pine or sweetgum

Root length density (RLD) and root biomass density (RBD) of fine roots (<2 mm) were examined in a factorial combination of loblolly pine (Pinus taeda L.) and broomsedge (Andropogon virginicus L.) and a factorial combination of sweetgum (Liquidambar styraciflua L.) and broomsedge to determine the extent to which competition may influence belowground plant response. Broomsedge and sweetgum seedlings were planted, grown for 1 year, and cut before planting of pine seedlings. Sampling occurred 1 year after planting of pine. Broomsedge had a significant negative effect (p < 0.10) on RBD and RLD of sweetgum and loblolly pine in the upper 30 and 45 cm of soil, respectively. RLD and RBD of broomsedge increased with increasing broomsedge density (p < 0.10) and decreased with addition of either tree species, with sweetgum having a greater effect. Patterns in the effects of competitors on RBD and RLD were similar to those noted for aboveground biomass. Specific root length (SRL) of broomsedge was three and five times greater than that of sweetgum or loblolly pine, respectively (p < 0.05). The addition of interspecific competitors reduced the percentage of total RLD of pine and sweetgum and RBD of broomsedge in the 0- to 15-cm soil depth with a corresponding increase in the 15- to 30-cm depth.