Isoprene emissions and photosynthesis in three ferns – The influence of light and temperature

A study was designed to determine the rates of isoprene emission and photosynthesis in three fern species [ Dicksonia antarctica Labill., Thelypteris decursive-pinnata (Van Hall) Ching and Thelypteris kunthii (Desv.) Morton] and the independent influence of light and temperature on these processes. The plants were conditioned in a growth chamber and then transferred to a controlled environment gas-exchange chamber. Samples of the chamber atmosphere were collected; isoprene was concentrated cryo-genically and measured by gas chromatography. Only small amounts of isoprene were detected around the ferns in the dark. Isoprene emissions increased with increasing levels of photosynthetic photon flux density (PPFD) in all three species; 50% of the maximum emission occurred at PPFD levels of 130 to 500 μmol m−² s−¹. Maximum isoprene emissions occurred between 35 and 39°C which is a lower temperature maximum than reported for angiosperms and gymnosperms. The increased emissions with temperature were primarily associated with increased biosynthetic rates for isoprene. Carbon lost through isoprene accounted for 0.02 to 2.6% of the carbon fixed during photosynthesis, depending on the PPFD level, temperature and fern species.