Quantifying BVOC emission rates and variability of three temperate marine macrophytes

Biogenic Volatile Organic Compounds (BVOC), emitted by Earth’s ecosystems, affect several chemical processes in the atmosphere that have profound climate impacts. Despite their climate relevance, global BVOC-budget estimations are still inaccurate and especially emissions originating from our oceans are poorly constrained. Marine macrophytes (i.e. macroalgae and seagrass) are a large and widespread organismal group whose BVOC emission rates are especially poorly quantified. In this study we set out to shorten this knowledge gap by quantifying ex situ with a PTR-TOF-MS the BVOC emission rates of three temperate macrophytes (Zostera marina, Fucus vesiculosus and Ulva intestinalis). To capture and increase our understanding of the variability of macrophyte BVOC-emissions, our quantifications were duplicated in two marine regions that vastly differ from each other, the eastern Atlantic (Ireland) and northern Baltic Sea (Finland). The three macrophytes emitted a large variety of BVOCs as 166 compounds were in total identified. Although many BVOCS were emitted by all macrophytes, significant differences were found in the total emission profiles, both between and within-species. Interestingly, the seagrass Zostera exhibited significantly higher overall BVOC emission rates per unit weight than the two macroalgae but also revealed clearly differing within-species emission profiles between the two regions. Of individual compounds, dimethyl sulfide (DMS) was emitted at the highest rates, but many other compounds (e.g., sesquiterpenes, C10H21O+) also showed notable emission rates. Although the most emitted BVOCs are commonly investigated compounds (e.g., DMS and terpenoids), our results show that the BVOC emissions are spread out over a large number of different compounds, suggesting that future studies would benefit from targeting a wider range of BVOCs than currently. Our results highlight macrophytes as highly variable sources of BVOCs, whose better inclusion into marine BVOC budgets should be strived for. However, more reliable data is needed, and future research should also focus on investigating the dynamics driving macrophyte BVOC emissions, their variability and eventual fate in the environment.