BVOC emissions from Posidonia oceanica, the most abundant Mediterranean seagrass species.

Biogenic Volatile Organic Compounds (BVOCs) are important precursors of tropospheric atmospheric pollutants such as ozone and secondary organic aerosols. Thus, it is crucial to characterize BVOCs sources at regional and global scales. Marine environments, especially benthic ecosystems, are still overlooked although they can produce a wide range of BVOCs. In this study, BVOCs emissions from Posidonia oceanica, the main seagrass species in the Mediterranean Sea, were characterised over several days using dynamic enclosure systems. A total of 105 different compounds were detected through PTR-ToF-MS and GC-MS analyses (after checking compounds correspondence between both analyses) and included terpenoids (isoprene), sulfur- (dimethyl sulfide (DMS)), halogenenated- (chloromethane), and oxygenated compounds (methanol, acetone). High BVOCs emissions were measured (up to 10 and 4 μg.gDW-1.h-1 for DMS and acetone, respectively), in the same ranges reported for terrestrial plant species. Most BVOCs followed diurnal cycles with higher emissions during the day compared to night, although nocturnal emissions were also detected. Surprisingly, DMS emissions showed an opposite pattern with higher emissions at night. Uptakes were recorded for formic acid all through the day, at night for acetonitrile and only punctually for most other BVOCs. Our results strongly suggest that P. oceanica meadows are important contributors to the regional BVOCs budget in the Mediterranean basin.