Isoprenoid emission in hygrophyte and xerophyte European woody flora: ecological and evolutionary implications

Abstract

for moisture (EIVM) was used to describe plant hygrophily. Phylogenetic analysis was carried out, 37 at a broader taxonomic scale on 128 species, and then refined on strong isoprene emitters (Salix and 38Populus species) based on isoprene synthase gene sequences (IspS). 39 40Results. Isoprene emitters were significantly more common, and isoprene emission was higher in 41 hygrophilous EIVM classes, whereas monoterpene emitters were more widespread, and 42 monoterpene emission was higher, in xeric classes. However, when controlling for phylogeny, 43 isoprene emission was not associated with EIVM, possibly due to the large presence of Salicaceae 44 among hygrophilous isoprene emitters. Moreover, the distribution of isoprene emitters among 45 EIVM classes was not related to IspS-based phylogenesis in Populus and Salix, suggesting that the 46 gene has not undergone evolution linked to ecological pressure. In contrast, monoterpene emission 47 pattern is independent of phylogeny, suggesting that the evolution of monoterpenes is associated 48 with transitions to more xeric habitats. 49 50 Main conclusions. Our results reveal an interesting ecological pattern linking isoprenoids and 51 water availability. The idea is surmised that isoprene is a trait that i) evolved in plants adapted to 52 high water availability; ii) is replaced by more effective protection mechanisms, e.g. more stable 53 isoprenoids, in plants adapting to more xeric environments; iii) being strongly constrained by 54 phylogeny, persists in Salicaceae adapted to more xeric environments. 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 Leaves of many woody and perennial plants constitutively emit volatile isoprenoids (isoprene and 66 monoterpenes) to the atmosphere, at rates that often exceed 1-2% of the photosynthetic carbon 67 fixation, especially in stressed leaves (Loreto & Schnitzler 2010). Isoprene and monoterpenes are 68 formed from photosynthetic metabolism in the chloroplasts (Loreto & Schnitzler 2010). Generally, 69 either isoprene or monoterpenes are emitted but not both (Harrison et al. 2013). However, some 70 species (e.g. Myrtales) show significant storage of monoterpenes in specialized structures and these 71 species can emit both isoprene and monoterpenes (Niinemets et al. 2004). 72Isoprene is believed to play a role against thermal and oxidative stresses, possibly because of the 73 capacity of this molecule to stabilize thylakoidal membranes (Singsaas et al. 1997, Velikova et al. The emission of isoprene and monoterpenes is widespread across plant families (Harley et al. 79 1999). A recent study has indicated a strong phylogeographic signal for monoterpenes; the emission 80 of monoterpenes is qualitatively different in cork oaks across their distribution range in Europe 81 (Loreto et al. 2009). Alien species of Hawaii emit more monoterpenes than native one...

Isoprene emission in the monocot Arundineae tribe in relation to functional and structural organization of the photosynthetic apparatus

“…As all Arundineae species considered in this study are perennial, additional life history traits may play a role in determining isoprene emission. It has also been proposed that monoterpene emission replaces isoprene emission in species associated to xeric environments (Loreto et al, 2014b). Our results are in line with this notion, as the Arundineae species that were examined in this study are all riparian, with the possible exception of H. macra, the only species that does not emit isoprene.…”

“…The present study is the first to cover isoprene emission from a tribe of monocotyledonous plants. We used the Arundineae tribe as a case study, as this clade includes fastgrowing plants which are known as strong isoprene emitters, e.g., A. donax and P. australis (Loreto et al, 2014b), as well as closely related species.…”

“…However, a limited number of plant families synthesize isoprene, and systematic studies aiming to uncover taxonomic or phylogeographic patterns have not delivered clear results Monson et al, 2013;Loreto et al, 2014b;Loreto and Fineschi, 2015). Few plant genera only include isoprene-emitting species (e.g., Populus, Salix) (Loreto et al, 2014b).…”

“…However, a limited number of plant families synthesize isoprene, and systematic studies aiming to uncover taxonomic or phylogeographic patterns have not delivered clear results Monson et al, 2013;Loreto et al, 2014b;Loreto and Fineschi, 2015). Few plant genera only include isoprene-emitting species (e.g., Populus, Salix) (Loreto et al, 2014b). However, in many other cases, emitting and non-emitting species can be found in the same genus (e.g., various genera of Fabaceae) (Harley et al, 1999;Logan et al, 2000).…”

“…However, in many other cases, emitting and non-emitting species can be found in the same genus (e.g., various genera of Fabaceae) (Harley et al, 1999;Logan et al, 2000). Fast-growing plants are often strong isoprene emitters (Loreto and Fineschi, 2014) and the trait is often associated to perenniality (Dani et al, 2014) and with hydrophily (Loreto et al, 2014b). The nuclear isoprene synthase (IspS) gene codes for the only enzyme specific of the isoprene biosynthetic pathway.…”