Ginkgo leaf cuticle chemistry across changing pCO2 regimes

Abstract

Cuticles have been a key part of palaeobotanical research since the mid-19th Century. Recently, cuticular research has moved beyond morphological traits to incorporate the chemical signature of modern and fossil cuticles, with the aim of using this as a taxonomic and classification tool. For this approach to work cuticle chemistry would have to maintain a strong taxonomic signal, with a limited input from the ambient environment in which the plant grew. Here, we use attenuated total reflectance Fourier Transform infrared (ATR-FTIR) spectroscopy to analyse leaf cuticles from Ginkgo biloba plants grown in experimentally enhanced CO2 conditions, to test for the impact of changing CO2 regimes on cuticle chemistry. We find limited evidence for an impact of CO2 on the chemical signature of Ginkgo cuticles, which supports the use of chemotaxonomy for plant cuticular remains across geological timescales.

Geochemical Fingerprints of Ginkgoales Across the Triassic-Jurassic Boundary of Greenland

“…The question concerning the influence of pCO 2 on cuticle chemistry remains unresolved. A recent study by Jardine et al (2019) addressed this issue via a meticulous experiment to test for the effects of pCO 2 variations on Ginkgo biloba leaf cuticle chemistry. By using attenuated total reflectance Fourier transform IR spectroscopy on leaves from plants grown in chambers with enhanced pCO 2 conditions, they showed that pCO 2 had little effect on the cuticle chemistry (Jardine et al 2019).…”

“…A recent study by Jardine et al (2019) addressed this issue via a meticulous experiment to test for the effects of pCO 2 variations on Ginkgo biloba leaf cuticle chemistry. By using attenuated total reflectance Fourier transform IR spectroscopy on leaves from plants grown in chambers with enhanced pCO 2 conditions, they showed that pCO 2 had little effect on the cuticle chemistry (Jardine et al 2019). However, an experiment with limited short-term elevated pCO 2 in growth chambers may not accurately reflect the influence on Ginkgoales cuticle in the past, such as in the Mesozoic greenhouse world, when plants were both adapted to and grew naturally over many generations under highly elevated pCO 2 .…”

“…In addition to morphological characters, studies of remnant organic constituents within fossils have shown to be important for supporting taxonomic and phylogenetic assignations (D'Angelo 2010(D'Angelo , 2015Vajda et al 2017) and even reconstructing overall architecture of fragmented fronds (D'Angelo et al 2018;Zodrow et al 2019). Infrared (IR) microspectroscopy has proven to be a particularly useful technique for this purpose because of its nondestructive nature, chemical specificity, and ability to analyze minute sam-ple areas, which enables analysis of, for instance, fossil pollen and spores (e.g., Steemans et al 2010;Fraser et al 2012;Jardine et al 2016Jardine et al , 2019Dupont-Nivet 2021), minute leaf fragments (Vajda et al 2017), fossil resin (Seyfullah et al 2015), and even fossilized cellular organelles (Qu et al 2019). IR microspectroscopy has been employed for the identification of organic compounds in various fossils, such as pre-Cambrian stromatolites and fungi (Qu et al 2015), but also for advanced multicellular organisms.…”

“…On the other hand, given similar preservation states, chemical differences between the fossil cuticles of various plants may reflect original compositional differences of the cuticle and even aid in resolving taxonomic relationships between plant groups (D'Angelo and Zodrow 2015). Furthermore, IR microspectroscopy has been applied to assess cuticular chemical variations in extant plants upon exposure to environmental triggers, such as increased levels of UV at high altitudes (Lomax et al 2012), heat stress (Liu et al 2019), and contrasting levels of atmospheric carbon dioxide concentration (pCO 2 ) under changing climates (Jardine et al 2019). Fraser et al (2011) conducted a study on the relationship between the UVB regime and aromatic pigment content in modern pollen and could show that birch pollen biochemically adapt to their local UV environment.…”

Functional traits of fossil plants

“…2j); these analyses yield chemo‐ecological data in relation to plant–insect interactions via chemical signaling to pollinators, seed dispersers, and prey and on secondary metabolites defense against UV‐B radiation (reviewed in García‐Plazaola et al ., 2015; Leide et al ., 2020). For example, strong autofluorescence in the blue (emission at 475 nm) under excitation with UV light (360 nm) can signal the presence of UV‐protecting compounds such as coumarin (García‐Plazaola et al ., 2015; Jardine et al ., 2019).…”