The role of petrichor – the scent of rain – in desert ecosystems and consequences under global warming

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In desert ecosystems, temporal dynamics are separated by wet-dry cycles, which are increasingly disturbed by Climate Change. Rainfall in desert ecosystems initiates an immediate CO2-burst together with substantial emissions of petrichor, 'the smell of rain'. This earthy smell is composed of various volatile organic compounds (VOCs), which travel with the wind for considerable distances. The water droplets in contact with dry soils elicit the release of previously sorbed VOCs and induce bacteria and fungi to produce VOCs de novo. Sixty years after the first description of petrichor, still little is known about its role in soil ecology and its relevance to atmospheric chemistry.Biotic interactions among members of soil microbial communities occur by exchanging signal molecules. Volatile signals act at greater spatial scale than soluble compounds and are increasingly recognized as crucial infochemicals to mediate intra- and interspecific interactions among soil microbiota. Yet, little is known on the specific functions of VOCs and their roles in mediating organism interactions, particularly in drylands.Emissions of petrichor from arid regions such as the Negev Desert (Israel) are likely to change in the near future as precipitation is projected to change by ~40% by 2050. Biogenic VOCs – particularly terpenoids and benzenoids – are essential players in atmospheric chemistry, influencing climate through cloud formation and the genesis of secondary organic aerosols, which absorb and scatter radiant energy. Soil microbial communities dominate desert ecosystems that span over 20% of the earth's surface. Therefore, there is an urgent need to consider the role of desert soil microbial communities in atmospheric chemistry. Our aim is to understand the sources, regulatory mechanisms, and controlling factors of VOC emissions in desert ecosystems which are paramount for building comprehensive global climate projection models. To this end, we aim to quantify and characterize changes in the petrichor composition along an aridity gradient in the Negev Desert (Israel), identify the entire activated microbial community (Eukaryota, Prokaryota, Archaea) after rain events in the desert biocrusts and in deeper soil layers, identify candidate producer and responsive taxa to VOCs by network analysis, and verify the roles of VOCs by targeted experiments with microbial isolates and by applying inhibitors of main petrichor VOCs to soils. Finally, we aim to upscale the global implications of petrichor emissions from desert ecosystems under future precipitation regimes.