Effects of light intensity on the production of VSLs from the marine diatom Ditylum brightwellii

Very short-lived substances (VSLs) are known to play an important role in ozone depletion in the troposphere and stratosphere. Environmental factors that influence the production of these compounds by marine phytoplankton, which is known to be the source of these compounds in open oceans, have not yet been well studied. Here we examined the effects of light intensity on the production of VSLs by the marine diatom Ditylum brightwellii. Bromodichloromethane (CHBrCl2), dibromochloromethane (CHBr2Cl), bromoform (CHBr3), chloroform (CHCl3), and dibromomethane (CH2Br2) in cultures incubated under full spectrum daylight intensities of 30, 60, and 120 mu mol photons m(- 2) s(- 1) were measured using purge and trap gas chromatograph-mass spectrometry. Phytoplankton growth was monitored by measuring chlorophyll-a concentration and cell density. Both the chlorophyll-a concentration (the cell density) and the production rates of VSLs increased with increasing light intensity. The maximum production rates of CHBrCl2, CHBr2Cl, CHBr3, CHCl3, and CH2Br2 were observed during the exponential or stationary phase, with the exception of CH2Br2 incubated under 30 mu mol photons m(- 2) s(- 1). The chlorophyll a-normalized (or cell-normalized) production rates of VSLs increased with increasing light intensity, e.g., the maximum of chlorophyll a-normalized production rates of CHCl3 under light intensities of 30, 60 and 120 mu mol photons m(- 2) s(- 1) were 0.06, 0.46 and 1.84 mu mol (g chlorophyll a) (-1) day(- 1), respectively. Our results suggest that marine diatoms are one of the significant sources of VSLs and that light intensity is a significant factor in estimating VSLs emissions from the open ocean.

Automated summary

This study found that the production rates of Very short-lived substances (VSLs) by marine diatom Ditylum brightwellii increased with higher light intensity, and there was a positive correlation between VSLs production and chlorophyll-a concentration and cell density.