The Production and Consumption of Volatile Organic Compounds in Soil and Decomposing Litter

Date The final copy of this thesis has been examined by the signatories, and we Find that both the content and the form meet acceptable presentation standards Of scholarly work in the above mentioned discipline. The production and consumption of volatile organic compounds in soil and decomposing litter Thesis directed by Associate Professor Noah Fierer Non-methane biogenic volatile organic compounds (BVOCs) are reactive, low molecular weight gases that play key roles in atmospheric chemistry, and in soils, where they can alter the rates of biogeochemical cycles and impact the growth of plants and soil organisms. However, the types and quantities of BVOCs released from or taken up by soils and decomposing litter remain poorly characterized as do the biotic and abiotic controls on these fluxes. We used proton transfer reaction mass spectrometry (PTR-MS) to quantify BVOC flux rates from decomposing litter under varying biotic and abiotic conditions. Microbial production was the primary source of BVOCs emitted from decomposing litter, while the types of BVOCs emitted from the litter differed in a predictable manner among litter types. The amount of carbon (C) emitted as VOCs from the some decomposing litter types was near equivalent to the amount emitted as CO2 from microbial respiration. Although nitrogen (N) amendments have been shown to increase CO2 emission rates from decomposing litter, we found that N amendments reduced BVOC emissions to near zero. We also examined BVOC fluxes in soil and litter under field conditions, quantifying the contribution of tree roots to flux rates. Tree roots, directly or indirectly, contributed to half of the total C emitted from the soil as BVOCs. Methanol was the BVOC emitted at the highest net rates in all studies, while isoprene was net consumed into the intact soil at the highest rates. This finding led us to investigate the microbial community involved in the consumption of isoprene. Using amplicon sequencing and experimental amendments of incubating soil with isoprene, we found that several phyla, known to consume other iv hydrocarbons, were responding positively to increasing isoprene concentrations. These microorganisms were able to consume approximately 70% of the isoprene added into the headspace of incubating soils, with consumption rates up to 770 pmol g-1 h-1. Together these results have increased or understanding of the biotic and abiotic controls on the consumption and production of BVOCs in the soil environment and these results highlight the importance of considering these effects when modeling …