Isoprene emission from phytoplankton monocultures: the relationship with chlorophyll-a, cell volume and carbon content

Abstract

Environmental context. Isoprene, a natural product of both terrestrial vegetation and marine organisms, is rapidly oxidised in the atmosphere, and thereby plays a key role in the regional budget of oxidants. Although isoprene production from terrestrial plants has been extensively investigated, production processes and emission rates from marine species are still poorly understood. We present results from laboratory experiments showing that isoprene is emitted from living phytoplankton cells at variable rates depending on the light intensity, cell volume, and carbon content of the plankton cells.Abstract. We report here isoprene emission rates determined from various phytoplankton cultures incubated under PAR light which was varied so as to simulate a natural diel cycle. Phytoplankton species representative of different phytoplankton functional types (PFTs) namely: cyanobacteria, diatoms, coccolithophorides, and chlorophytes have been studied. Biomass normalised isoprene emission rates presented here relative to the chlorophyll-a (Chl-a) content of the cultures showed that the two cyanobacteria (Synechococcus and Trichodesmium) were the strongest emitters with emission rates in the range of 17 to 28 mg C 5 H 8 g À1 Chl-a h À1 . Diatoms produced isoprene in a significantly lower emission range: 3 to 7.5 mg C 5 H 8 g À1 Chl-a h À1 and Dunaliella tertiolecta was by far the lowest emitter of our investigated plankton cultures. Despite the group specific differences observed, a high emission rate variance was observed to occur within one phytoplankton group. However, a combination of literature and our own data showed a clear relationship between the actual cell volume and the isoprene emission rates. This relationship could be a valuable tool for future modelling approaches of global isoprene emissions.

Marine isoprene production and consumption in the mixed layer of the surface ocean – a field study over two oceanic regions

“…During SPACES, with lower ocean temperatures and lower light levels than OASIS, the production rate is higher. This relationship would confirm the findings of two independent laboratory studies of Bonsang et al (2010) and Shaw et al (2003). Bonsang et al (2010) tested two species of cyanobacteria at 20 • C and found higher isoprene production rates than a different species tested by Shaw et al (2003) at 23 • C and even stronger light intensities.…”

“…This relationship would confirm the findings of two independent laboratory studies of Bonsang et al (2010) and Shaw et al (2003). Bonsang et al (2010) tested two species of cyanobacteria at 20 • C and found higher isoprene production rates than a different species tested by Shaw et al (2003) at 23 • C and even stronger light intensities. However, Exton et al (2013) measured the same rate as Shaw et al (2003) at 26 • C for one species, but a 5-times-higher production rate for another species at the same temperature.…”

“…These literature studies showed that isoprene production rates are light dependent, with increasing production rates at higher light levels (Shaw et al, 2003;Gantt et al, 2009;Bonsang et al, 2010;Meskhidze et al, 2015). To include the light dependency in our calculations, we followed the approach of Gantt et al (2009) for each PFT by applying a log-squared fit between all single literature laboratory chl-a-normalized isoprene production rates P chloro (µmol isoprene (g chl a) −1 h −1 ) (references in Table 2) and their measured light intensity I (µmol m −2 s −1 ) during individual experiments to determine an emission factor (EF) for each PFT ( Fig.…”

Dissolved organic matter (DOM) release by phytoplankton in the contemporary and future ocean

“…Shaw et al (2003) also measured the production of a range of light non-methane hydrocarbons (C 2 to C 6 ); however, only isoprene was consistently produced by the five phytoplankton species studied. Bonsang et al (2010) grew a range of phytoplankton species, representing different major phylogenetic groups (cyanobacteria, diatoms, coccolithophores and chlorophytes), in laboratory cultures. All the phytoplankton investigated emitted isoprene, with the highest production rates (per unit chlorophyll a) occurring in the cyanobacteria (Trichodesmium and Synechococcus) and the lowest in the chlorophyte Dunaliella tertiolecta.…”

Ocean-Atmosphere Interactions of Gases and Particles

“…Different PFTs have distinct impacts on the marine food web and biogeochemical cycling, e.g. variable relationships of different PFTs to isoprene production have been observed in laboratory experiments (Bonsang et al 2010). Ocean colour satellite observation is restricted to the near-surface layer, which varies from meters to about 60 m thick depending on the presence of optically-significant water constituents and the wavelength considered (Smith and Baker 1978).…”