Quantifying environmental stress-induced emissions of algal isoprene and monoterpenes using laboratory measurements

Abstract. We report here production rates of isoprene and monoterpene compounds (α-pinene, β-pinene, camphene and d-limonene) from six phytoplankton monocultures as a function of irradiance and temperature. Irradiance experiments were carried out for diatom strains (Thalassiosira weissflogii and Thalassiosira pseudonana), prymnesiophyte strains (Pleurochrysis carterae), dinoflagellate strains (Karenia brevis and Prorocentrum minimum), and cryptophyte strains (Rhodomonas salina), while temperature experiments were carried out for diatom strains (Thalassiosira weissflogii and Thalassiosira pseudonana). Phytoplankton species, incubated in a climate-controlled room, were subject to variable light (90 to 900 μmol m⁻² s⁻¹) and temperature (18 to 30 °C) regimes. Compared to isoprene, monoterpene emissions were an order of magnitude lower at all light and temperature levels. Emission rates are normalized by cell count and Chlorophyll a (Chl a) content. Diatom strains were the largest emitters, with ~ 2 × 10⁻¹⁷ g(cell)⁻¹h⁻¹ (~ 35 μg (g Chl a)⁻¹ h⁻¹) for isoprene and ~ 5 × 10⁻¹⁹ g (cell)⁻¹ h⁻¹ (~ 1 μg (g Chl a)⁻¹) h⁻¹) for α-pinene. The contribution to the total monoterpene production was ~ 70% from α-pinene, ~ 20% for d-limonene, and < 10% for camphene and β-pinene. Phytoplankton species showed a rapid increase in production rates at low irradiance (< 150 μmol m⁻² s⁻¹) and a gradual increase at high (> 250 μmol m⁻² s⁻¹) irradiance. Measurements revealed different patterns for time-averaged emissions rates over two successive days. On the first day, most of the species showed a distinct increase in production rates within the first 4 h while, on the second day, the emission rates were overall higher, but less variable. The data suggest that enhanced amounts of isoprene and monoterpenes are emitted from phytoplankton as a result of perturbations in environmental conditions that cause imbalance in chloroplasts and force primary producers to acclimate physiologically. This relationship could be a valuable tool for development of dynamic ecosystem modeling approaches for global marine isoprene and monoterpene emissions based on phytoplankton physiological responses to a changing environment.