Isoprene emission predominates over the others biogenic Volatile Organic
Compounds, especially in tropical forests. This compound influences on atmospheric chemistry and carbon balance. Isoprene emission is induced by environmental factors such as light and temperature. Thus, it is important to have investigations about isoprene production and emission in tropical species related to the environmental factors, making it necessary in order to improve regional or global models and detailed understanding of the possible contributors to global climate change. This study aimed to identify and quantify the isoprene emission and photosynthesis at different levels of light intensity and temperature, in three phenological phases (late mature leaf - FMT, old leaf - FV, and young mature leaf - FMR) of Eschweilera coriacea (Matamatá verdadeira), since this species shows the most distribuition in the Amazon. Photosynthesis measurements were carried out between 8 and 12 h, using a commercial portable photosynthesis system (LI-6400, LI-COR, Inc, Lincoln, NE, USA). To measure isoprene emissions, air exiting the LI-6400 leaf chamber was routed to fill a X-liter Teflon bag. Isoprene concentrations in the bag were then determined using a Proton Transfer Reaction Mass Spectrometer (PTR-MS; Ionicon Analytik, Innsbruck, Austria). The collections for both procedures were performed at different levels of irradiance intensities (from 0 to 2000 μmol m-2 s-1) and leaf temperature was varied between approximately 25 °C and 45 °C. . Results showed that FMR had the highest photosynthesis and isoprene emission rates at all light intensity and leaf temperatures, followed by FMT and FV. This suggests that aging favors the reduction of the leaf photosynthetic activity and the isoprene production and emission. In relation to the saturation irradiance, photosynthesis showed saturation levels lower than isoprene emission. Isoprene emission increased until 2000 μmol m-2 s-1 of irradiance. The optimal temperatures were demonstrated between 32 and 37.5°C in all three leaf phases for photosynthesis, and optimal temperatures for isoprene emission were higher than approximately 39.5°C. Photosynthesis was more sensitive to the warming effect, while for isoprene emission was suggested that it could increase even at temperatures greater than those presented. Thus, the results suggest thermotolerance hypothesis to photosynthesis, provided by isoprene production and emission. These results agree to the arguments which isoprene decreases damage caused by high temperatures; this compound is light dependent; isoprene emission is related to the leaf carbon balance; and that knowledge of changes in isoprene emission due to light and temperature variations may contribute to understand atmosphere chemistry reactions.
