Abstract
Herbarium samples are increasingly being recognized for their potential in answering a wide range of research questions. However, the suitability of herbarium samples for chemical analysis is largely unexplored as they are thought to be too degraded. The aim of this study was to explore terpenoid profiles across time and geographic space for four medicinal species of Salvia across the Mediterranean to assess the suitability of using herbarium specimens in chemical analyses. Herbarium samples of Salvia aethiopis, S. multicaulis, S. officinalis, and S. sclarea collected over 150 years across the Mediterranean were compared to modern samples using both targeted and untargeted gas chromatography-mass spectrometry analysis of terpene profiles. There was no effect of collection year on chemical composition, although the total concentration of the 20 assessed standards and two individual standards significantly decreased over time. Instead, chemical profiles were defined by species, with strong species effects identified on both the targeted and untargeted chemical composition. Geographic variation was a factor in regulating the untargeted chemical compositions, suggesting some underlying environmental effects. However, there was no effect of sample altitude on either the targeted or untargeted chemical compositions. Chemical composition of four Salvia species are predominantly defined by species, and there was a substantially smaller effect of year of sampling. Given these results herbarium collections may well represent a considerably underused resource for chemical analyses that can benefit biodiversity and other studies.
Highlights
Herbarium collections are increasingly being recognized as a unique, verifiable, and underused resource of big data across time and space for a variety of research questions (Lavoie, 2012; Funk, 2014; Rønsted et al, 2017; Cardoso et al, 2018; James et al, 2018)
Borneol was the most abundant compound, ranging from 172 to 96,234 ng/μL, and were significantly higher in S. officinalis (31,954 μg/g) and S. multicaulis (21,964 μg/g) than averages in S. sclarea (436 μg/g), and S. aethiopis (675 μg/g) (Table 2). p-cymene was the second most abundant compound that was concentrated in S. officinalis (11,559 μg/g) and S. multicaulis (6,774 μg/g) when compared to S. sclarea (51 ng/μL) and S. aethiopis (47 μg/g)
Whilst camphor was present in lower abundance than borneol and p-cymene in S. officinalis (8291 μg/g) and S. multicaulis (5,273 μg/g), it was present in comparable quantitates in S. sclarea (3,246 μg/g) and in two of the five S. aethiopis samples
Summary
Herbarium collections are increasingly being recognized as a unique, verifiable, and underused resource of big data across time and space for a variety of research questions (Lavoie, 2012; Funk, 2014; Rønsted et al, 2017; Cardoso et al, 2018; James et al, 2018). Herbarium collections offer an accessible source of specimens for a plethora of research questions compared to field expeditions (Bebber et al, 2010; Hardion et al, 2014; Xu et al, 2015). Herbarium specimens are records in time and space and represent several 100 years of collection history across the globe, including species rare and extinct or gone habitats (Silva et al, 2017) that provide possibilities not available using only modern samples. Collections provide a time window into the past allowing exploration of changes in composition of floras (Calinger, 2015), distribution of invasive weeds or threatened species (Rivers et al, 2011; Martin et al, 2016), changes in flowering times (Davis et al, 2015) or leaf-out times (Everill et al, 2014) in response to climate change as well as to model predictions of future trends (James et al, 2018).
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