Microbial consumption of atmospheric isoprene in a temperate forest soil

Isoprene (2-methyl-1,3 butadiene) is a low-molecular-weight hydrocarbon emitted in large quantities to the atmosphere by vegetation and plays a large role in regulating atmospheric chemistry. Until now, the atmo-sphere has been considered the only significant sink for isoprene. However, in this study we performed both in situ and in vitro experiments with soil from a temperate forest near Ithaca, N.Y., that indicate that the soil provides a sink for atmospheric isoprene and that the consumption of isoprene is carried out by microorgan-isms. Consumption occurred rapidly in field chambers (672.60 6 30.12 to 2,718.36 6 86.40 pmol gdw21 day21) (gdw is grams [dry weight] of soil; values are means 6 standard deviations). Subsequent laboratory experi-ments confirmed that isoprene loss was due to biological processes: consumption was stopped by autoclaving the soil; consumption rates increased with repeated exposure to isoprene; and consumption showed a tem-perature response consistent with biological activity (with an optimum temperature of 30°C). Isoprene con-sumption was diminished under low oxygen conditions (120 6 7.44 versus 528.36 6 7.68 pmol gdw21 day21 under ambient O2 concentrations) and showed a strong relationship with soil moisture. Isoprene-degrading microorganisms were isolated from the site, and abundance was calculated as 5.8 3 105 6 3.2 3 105 cells gdw21. Our results indicate that soil may provide a significant biological sink for atmospheric isoprene. Isoprene (2-methyl-1,3 butadiene [C5H8]), is a low-molecu