MICROBIAL CONSUMPTION OF ATMOSPHERIC ISOPRENE IN A TEMPERATE FOREST SOIL

Isoprene (2-methyl-1,3 butadiene) is a low-molecular-weight hydrocarbo n emitted in large quantities to the atmosphere by vegetation and play s a large role in regulating atmospheric chemistry. Until now, the atm osphere has been considered the only significant sink for isoprene, Ho wever, in this study we performed both in situ and in vitro experiment s with soil from a temperate forest near Ithaca, N,Y,, that indicate t hat the soil provides a sink for atmospheric isoprene and that the con sumption of isoprene is carried out by microorganisms. Consumption occ urred rapidly in field chambers (672.60 +/- 30.12 to 2,718.36 +/- 86.4 0 pmol gdw(-1) day(-1)) (gdw is grams [dry weight] of soil; values are means +/- standard deviations). Subsequent laboratory experiments con firmed 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 temperature r esponse consistent with biological activity (with an optimum temperatu re of 30 degrees C), Isoprene consumption was diminished under low oxy gen conditions (120 +/- 7.44 versus 528.36 +/- 7.68 pmol gdw(-1) day(- 1) under ambient O-2 concentrations) and showed a strong relationship with soil moisture. Isoprene-degrading microorganisms were isolated fr om the site, and abundance was calculated as 5.8 x 10(5) +/- 3.2 x 10( 5) cells gdw(-1). Our results indicate that soil may provide a signifi cant biological sink far atmospheric isoprene.