4. Discussion
Past studies have examined constitutive leaf isoprenoid emission from tropical trees with a focus on isoprene (e.g. Keller & Lerdau 1999; Harley et al. 2004; Kuhn et al. 2004b; Pegoraro, Rey, Abrell, Haren & Lin 2006; Alves, Harley, Gonçalves, Silva & Jardine 2014; Jardine et al. 2014, 2016; Taylor, Smith, Slot & Feeley 2019), followed by monoterpenes (e.g. Kuhn et al. 2004a; Jardineet al. 2017, 2020). These past studies offered meaningful insights on how isoprene and monoterpenes respond to light, temperature and drought, and how they might be related to plant stress tolerance. Still, constitutive sesquiterpene emission has only been shown from tropical species in one study in Borneo (Llusia, Sardans, Niinemets, Owen & Peñuelas 2014), and therefore most of our scarce knowledge on sesquiterpenes produced by tropical species comes from the content of these compounds either in leaf or resins (e.g. Salazar et al.2018), which only configures the potential for induced emissions. In this study, we observed that Amazonian hyperdominant tree species emit isoprene, monoterpenes and sesquiterpenes in a light-dependent manner (constitutively), and that the amount and proportion of emissions change seasonally. The plasticity of emission capacity and chemical composition of isoprenoids emitted by trees distributed across different forest types, their seasonal behavior, and the significance of our findings are discussed in the following sections.