Sources, controls, and significance of soil geosmin emissions in dryland ecosystems

If you have spent time in deserts, you are likely familiar with petrichor — the ‘smell of rain’ — the earthy scent characteristic of soil rewetting events. Temporal dynamics in desert ecosystems are characterized by such sudden rain events and the associated emissions of petrichor. One of the key compounds contributing to petrichor is geosmin, a terpenoid volatile organic compound produced by soil microbes. Although geosmin was discovered over 50 years ago, its biological and ecological functions are still unknown. The specific microbes responsible for geosmin emissions from soil are undetermined and we currently lack a comprehensive understanding of how geosmin emissions vary temporally and spatially across dryland ecosystems. Most notably, although preliminary evidence suggests that geosmin can strongly influence the activities and interactions of both macro—and micro—organisms, the specific nature of these volatile—mediated impacts remains unresolved, despite their likely importance in arid ecosystems. This project will use a series of experimental studies conducted on soils collected from southern Israel and the southwestern U.S. to quantify how geosmin emissions vary as a function of soil and site characteristics, identify the microbial sources of geosmin, determine the environmental controls on geosmin emissions, and identify how exposures to geosmin can influence microbial and plant communities in dryland ecosystems.

Although volatile organic compounds (VOCS) are increasingly recognized as being important in belowground systems, the specific nature of these emissions and the associated consequences for soil biota remain poorly understood. This project focuses on one such VOC, geosmin — a microbially—produced metabolite often emitted in high concentrations from desert soils following rain events. This project will examine geosmin emissions across aridity gradients, the specific taxa responsible for the production of this volatile, and the controls on emission rates. Moreover, this project will test the hypothesis that geosmin acts as a signaling molecule with wide—ranging effects on the activities of microbes and plants in desert ecosystems. Together this work will advance our understanding of a widely-observed, but little—understood, phenomenon in desert soils that is likely to have important consequences for understanding biotic responses to rewetting events in arid environments. As such, this work is likely to be relevant to researchers in disciplines ranging from ecosystem ecology to microbiology to soil science.