Impact of phytoplankton blooms on marine VOCs emission

Volatile organic compounds (VOCs) are diverse bioactive molecules of low molecular weight and high vapor pressure. VOCs are produced by biotic and abiotic processes and are important for atmospheric chemistry as main biogenic precursors of secondary organic aerosols. In marine environments, the phytoplankton are the main source of marine VOCs, which appear to be an important source of organic compounds fueling bacterioplankton growth. Increased eutrophication and rising temperatures will likely increase intensity of coastal phytoplankton blooms in the coming decades with the potential cascading consequence of elevated VOC production rates and emissions. To assess VOC production by a phytoplankton bloom, we conducted a mesocosm experiment where VOC production by natural, unaltered microbial communities were compared to that by a phytoplankton bloom induced by nutrient amendment. VOCs were measured by combining a purge-and-trap system with a high-sensitivity proton-transfer reaction time-of-flight mass spectrometer (PTR-TOF-MS). Using 16S rRNA and 18S rRNA sequencing data, we analyzed the prokaryote and eukaryote community composition and the effect of their relationships on the VOC composition and concentration. The concentration and composition of VOCs changed over the course of the phytoplankton bloom, and some VOCs were significantly higher in the phytoplankton bloom than in the unaltered microbial communities.  A strong and significant correlation was found between the bacterial and eukaryotic communities, and VOCs. In addition, permutation analysis showed how the relationships between phytoplankton and bacteria can modify the composition of VOCs. These results evidence the effect of phytoplankton-bacteria relationships in marine VOC emissions.