Abstract
Extreme weather and globalisation leave our climate vulnerable to invasion by alien species, which have negative impacts on the economy, biodiversity, and ecosystem services. Rapid and accurate identification is key to the control of invasive alien species. However, visually similar species hinder conservation efforts, for example hybrids within the Japanese Knotweed complex.We applied the novel method of ATR-FTIR spectroscopy combined with chemometrics (mathematics applied to chemical data) to historic herbarium samples, taking 1580 spectra in total. Samples included five species from within the interbreeding Japanese Knotweed complex (including three varieties of Japanese Knotweed), six hybrids and five species from the wider Polygonaceae family. Spectral data from herbarium specimens were analysed with several chemometric techniques: support vector machines (SVM) for differentiation between plant types, supported by ploidy levels; principal component analysis loadings and spectral biomarkers to explore differences between the highly invasive Reynoutria japonica var. japonica and its non-invasive counterpart Reynoutria japonica var. compacta; hierarchical cluster analysis (HCA) to investigate the relationship between plants within the Polygonaceae family, of the Fallopia, Reynoutria, Rumex and Fagopyrum genera.ATR-FTIR spectroscopy coupled with SVM successfully differentiated between plant type, leaf surface and geographical location, even in herbarium samples of varying age. Differences between Reynoutria japonica var. japonica and Reynoutria japonica var. compacta included the presence of two polysaccharides, glucomannan and xyloglucan, at higher concentrations in Reynoutria japonica var. japonica than Reynoutria japonica var. compacta. HCA analysis indicated that potential genetic linkages are sometimes masked by environmental factors; an effect that can either be reduced or encouraged by altering the input parameters. Entering the absorbance values for key wavenumbers, previously highlighted by principal component analysis loadings, favours linkages in the resultant HCA dendrogram corresponding to expected genetic relationships, whilst environmental associations are encouraged using the spectral fingerprint region.The ability to distinguish between closely related interbreeding species and hybrids, based on their spectral signature, raises the possibility of using this approach for determining the origin of Japanese knotweed infestations in legal cases where the clonal nature of plants currently makes this difficult and for the targeted control of species and hybrids. These techniques also provide a new method for supporting biogeographical studies.
Highlights
Invasive alien species (IAS), such as Japanese Knotweed, detrimentally impact the economy [1], ecosystem services [2], and native flora [3]
ATR-FTIR spectroscopy was used to explore the relationship between sample types, and to determine whether herbarium samples remain tractable to this type of analysis decades after collection
The present study clearly demonstrates the power of this approach for the analysis of historic herbarium samples, fresh samples taken from plants grown together under controlled conditions prior to spectral acquisition would remove ‘environment’ as a variable to allow an unfettered comparison between plant types
Summary
Invasive alien species (IAS), such as Japanese Knotweed, detrimentally impact the economy [1], ecosystem services [2], and native flora [3]. The impacts of IAS are set to worsen as an increasing human population heightens the demand for healthy crops [4], whilst globalisation [5] and extreme weather events [6] create further opportunities for introduction and spread of invasives. Hybridisation is a strategy employed by IAS to overcome a genetic bottleneck [11]. It results in ‘heterosis’, the production of offspring with increased ‘hybrid vigour’ [12]. Hybrid descendants may have improved traits relative to their parents such as invasiveness [11], growth rate, reproductive success and yield [13], genetic variance [14], and stress tolerance e.g. to herbicides [15] and cold [16]
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