Isoprene emissions from a tundra ecosystem

Abstract

Whole-system fluxes of isoprene from a moist acidic tundra ecosystem and leaf-level emission rates of isoprene from a common species (<i>Salix pulchra</i>) in that same ecosystem were measured during three separate field campaigns. The field campaigns were conducted during the summers of 2005, 2010 and 2011 and took place at the Toolik Field Station (68.6&deg; N, 149.6&deg; W) on the north slope of the Brooks Range in Alaska, USA. The maximum rate of whole-system isoprene flux measured was over 1.2 mg C m⁻² h⁻¹ with an air temperature of 22 °C and a PAR level over 1500 μmol m⁻² s⁻¹. Leaf-level isoprene emission rates for <i>S. pulchra</i> averaged 12.4 nmol m⁻² s⁻¹ (27.4 μg C gdw⁻¹ h^&minus;1) extrapolated to standard conditions (PAR = 1000 μmol m⁻² s⁻¹ and leaf temperature = 30 &deg;C). Leaf-level isoprene emission rates were well characterized by the Guenther algorithm for temperature with published coefficients, but less so for light. Chamber measurements from a nearby moist acidic tundra ecosystem with little <i>S. pulchra</i> emitted significant amounts of isoprene, but at lower rates (0.45 mg C m⁻² h^&minus;1) suggesting other significant isoprene emitters. Comparison of our results to predictions from a global model found broad agreement, but a detailed analysis revealed some significant discrepancies. An atmospheric chemistry box model predicts that the observed isoprene emissions have a significant impact on Arctic atmospheric chemistry, including a reduction of hydroxyl radical (OH) concentrations. Our results support the prediction that isoprene emissions from Arctic ecosystems will increase with global climate change.