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SOIL BIOLOGY & BIOCHEMISTRY

Volatile Organic Metabolites as Indicators of Soil Microbial Activity and Community Composition Shifts

^a Dep. of Geosciences, Mississippi State Univ., PO Box 5448, Mississippi State, MS, 39762
^b Dep. of Geology and Geophysics, Texas A&M Univ., College Station, TX 77843

^* Corresponding author (karen.mcneal{at}msstate.edu).

The dynamics of soil microorganisms have important implications for the response of subsurface soil ecosystems to perturbations. Traditional indicators such as functional, community, activity, and carbon and nutrient pathway methods have been used to characterize soil microbial processes and ecological function; however, many of these indicators lack the ability to measure changes over large (e.g., landscape) spatiotemporal scales in soil environments. This research introduces the analysis of soil volatile organic compound (VOC) metabolites as nondestructive indicators of subsurface microbial activity and community composition as a function of varying environmental factors. Results of method validation using laboratory microcosms are presented, where VOC metabolites as characterized by gas chromatography and mass spectrometry (GC–MS) were related to CO₂ evolution as a measure of microbial activity and to community-level physiological profiles (CLPPs) and fatty acid methyl ester (FAME) community structure techniques. Results included the identification of 72 VOC metabolites produced from the soils, where significant ( < 0.05) differences in the estimated amounts and types of compounds produced were observed between treatments. Temporal measurements indicated similarity between VOC production and CO₂ evolution, where increased amounts over time were detected. Principal component analysis (PCA) and hierarchical cluster analysis showed that the VOC results clustered similarly to FAME and CLPP results. Our results suggest there is promise for the use of naturally produced VOCs as potential indicators of soil microbial ecosystems over large spatiotemporal dynamics and environmental perturbations.

Abbreviations: ATD, automated thermal desorber • CLPP, community-level physiological profiles • FAME, fatty acid methyl ester • GC–MS, gas chromatograph mass spectrometer • LANWR, Laguna Atascosa National Wildlife Refuge • PCA, principal component analysis • VOC, volatile organic compound