EMISSIONS OF NONMETHANE ORGANIC-COMPOUNDS AND CARBON-DIOXIDE FROM FOREST FLOOR CORES

Forest floor emissions of CO2 and non-methane volatile organic compounds (NMOCs) were measured to determine their contribution to C losses from forests. Forest floor cores 19 cm in diameter and approximately 10 cm deep were obtained from beneath loblolly pine (Pinus taeda L.), oak-maple (Quercus-Acer), and yellow-poplar (Liriodendron tulipifera L.) trees on the Walker Branch Watershed, Oak Ridge, TN. The cores were enclosed in an open system gas exchange instrument from which inlet and outlet concentrations of NMOC emissions were sampled. The NMOCs were quantified with a C trap/cryofocus/gas chromatography approach. Total NMOC emissions from the forest floor cores ranged from 15 to 90 nmol C m-2 s-1, and differed beneath each tree species. Cores from beneath yellow-poplar trees had nearly an order of magnitude greater C equivalent efflux than cores from beneath either the pine or oak-maple trees. Monoterpenes comprised virtually all of the NMOC emissions from the cores. The C equivalent efflux of NMOCs from the forest floor cores was one to two orders of magnitude less than rates of CO2 efflux (4-8 mumol m-2 s-1), indicating a very minor role for titter and soil NMOC emissions in stand C cycling.