Effects of desiccation dynamics on petrichor emissions in Negev Desert soils

Petrichor – a strong scent released from desiccated soil upon rewetting – is a mixture of volatile organic compounds (VOCs) that impact atmospheric chemistry and originates from the abiotic desorption of stored compounds and the de novo microbial production. The aridity gradient of the Negev Desert soils provides a particularly suitable system for studying petrichor emissions due to their distinctive and well-studied microbial communities (e.g., Actinobacteria and Cyanobacteria) but similar physical properties that control VOC physical evaporation, and absence of plant material as confounding sources of VOCs. While the chemical and microbial origins of petrichor are relatively well described, the controlling factors of its emission remain unclear. This study investigated the influences of desiccation dynamics on petrichor emissions and microbial succession in soils from an aridity gradient of the Negev Desert in Israel. Soil cores were subjected to three sequential rain events followed by contrasting desiccation regimes (long drought, rapid desiccation and slow desiccation) in a realistic climate simulation. Their VOC emissions and microbial metatranscriptomics were studied at five time points, including three upon rewetting and two during slow desiccation. The results showed that VOCs were produced during soil drying, with compound-specific release patterns occurring either during desiccation or upon rehydration. Despite having a common biosynthetic pathway, monoterpenoid and sesquiterpenoid emissions exhibited distinct temporal dynamics, suggesting different underlying physical control or microbial activity. The abundances and chemical diversity of petrichor decreased with increasing aridity, closely following the decline in microbial diversity. The microbial communities varied among rewetting scenarios and exhibited clear temporal succession during slow desiccation, likely regulating petrichor emissions through microbial activation. Greater community dispersion at 24 hours after rewetting indicated rapid and heterogeneous microbial reactivation, potentially contributing to increased variability and reduced predictability of early petrichor emissions. These findings highlighted the importance of desiccation rate in controlling petrichor emissions in desert ecosystems. Further field measurements and functional microbial analyses will be essential to understand how changing desiccation regimes will reshape petrichor emissions and the microbial communities in desert ecosystems.