Unraveling the chemistry of plant flammability: Exploring the role of volatile secondary metabolites beyond terpenes

Abstract

Plant flammability research has proven pivotalin comprehending the contribution of vegetation to the flammability of forestecosystems. Yet, the relationship between many leaf chemical traits and plant flammabilityis poorly understood. While terpenes and some leaf nutrients in plants havebeen extensively studied for their role in flammability, a wide array of othersecondary metabolites remain unexplored in this context. Here, we present thevolatile secondary metabolites composition of fresh leaves from nine dominantspecies from central Chile, both native and exotic, and determine whether thereis variability within and among species in chemical composition andflammability. Moreover, we investigate how these compounds influence variousleaf flammability traits. The Chilean Mediterranean ecosystem emerges as auseful study site given its unique endemic flora, increased frequency of forestfires, proliferation of invasive plants and extensive land conversion thatfavors the spread of fire-prone exotic species, and significant scarcity ofphytochemical research dedicated to this ecosystem. A total of 118 volatilechemical compounds were quantified, belonging to over ten groups of volatilesecondary metabolites. Terpenes, ketones, and hydrocarbons comprised 75 % ofthese compounds, and each species displayed a unique phytochemical profile.Surprisingly, some native species (Citronella mucronata,Cryptocarya alba) exhibitedequivalent or higher leaf flammability than the well-known flammable exotics Eucalyptus globulus and Pinus radiata, respectively. Leafflammability was best explained by the concentration of aldehydes, ketones,green leaf volatiles, and aromatic compounds. Interestingly, terpenes as wellas moisture content were not significantly correlated with flammability. Inconclusion, our results highlight the importance of considering a broader rangeof phytochemicals, beyond terpenes, to fully understand leaf flammability amongspecies. Consequently, a deeper understanding -within and across ecosystems- ofthe influence exerted by diverse groups of phytochemicals on flammability is anurgent need for forest management planning in an increasingly flammable world.