The palaeoecology of leaf chemistry

Plants have been central to life on land for over 400 million years, during which time environmental conditions have changed dramatically. Plants’ responses to changing environmental conditions can include changes in leaf chemistry, which encompasses:

  1. i) lignin, cellulose and other cell wall components, the most abundant organic polymers on the planet and a significant sink for photosynthetically fixed carbon (Shtein et al., 2018).
  2. ii) proteins, peptides and amino acids, an important aspect of nutritional value for herbivores (Ryalls et al., 2017).

iii) lipids, such as leaf wax n-alkyl compounds and triterpenoids, which provide physical and chemical protection for the plant and are widely used in palaeoclimate and palaeoenvironmental reconstructions (Diefendorf et al., 2012; Bush & McInerney, 2015).

Together, these chemical components determine the quality and reactivity of leaf organic matter, ultimately influencing terrestrial carbon sequestration, which can feed back to influence atmospheric composition (Pan et al., 2011). Changes in leaf chemistry driven by temperature, precipitation or other environmental variables have received limited attention, especially in temperate climates. Additionally, the utility of leaf chemistry to investigate plant response to environmental change in the Quaternary has not been fully investigated.

The aim of this project is to determine baseline leaf chemistry for a range of living fossil and native UK species and investigate how these species respond to changing environmental conditions along natural climate gradients. Leaf chemistry will be compared to other leaf traits (e.g. leaf mass per area, leaf shape) to determine if variations in leaf chemistry co-vary with other traits known to respond to environmental pressures (e.g Bacon et al., 2016; Wright et al., 2004). The project will also investigate leaf chemistry preservation in a range of Holocene sediment cores from arctic, temperate and tropical sites to determine if and how leaf chemistry tracks environmental change in these different locations over long timescales. This will allow us to investigate responses at specific locations, but also determine whether the relationships can be scaled up to global scale fluxes over long timescales.

Objectives:

You will work with scientists at the University of Leeds, National University of Ireland, Galway, and botanic gardens around the UK to quantify leaf chemistry changes over temperature/precipitation gradients and to understand how these signals can be used to interpret palaeoecology.
In particular, according to your particular research interests, the studentship could involve:

  1. Characterising leaf chemistry for “living fossil” taxa that have previously not been fully investigated e.g. Gingko biloba, Araucaria araucana.
  2. Evaluating the changes in leaf chemistry of selected taxa along climate gradients.
  3. Comparing leaf chemistry to other leaf traits associated with plant responses to environmental change (e.g. leaf mass per area, stomatal size and number)
  4. Investigating the leaf chemistry signal and its utility as a palaeoecological tool in a range of Holocene sediment and peat cores from arctic, temperate and tropical biomes form a large collection housed in the School of Geography.
  5. Investigate the implications of changes in leaf chemistry on the environment and carbon cycling under Holocene and future climate change, utilizing climate model simulations incorporating a dynamic vegetation model.

Potential for high impact outcome

The project will directly investigate the potential links between leaf chemistry and environmental change. The wider question that this project will contribute to is “How do changes in leaf organic matter (OM) quality associated with environmental changes affect the fate of that OM in the global carbon cycle?”. This has implications for understanding how terrestrial ecosystems have responded to past environmental change and how they may respond in the near and medium term future (Figure 1), making the research timely and likely to produce several outputs, including 3–4 publications, at least one of which we anticipate being suitable for submission to a high-impact journal.

Figure 1

Training

The student will work under the supervision of Dr. Fiona Gill and Dr Daniel Hill in the School of Earth and Environment and will be further co-supervised by Dr Karen Bacon, Botany & Plant Sciences, National University of Ireland, with the opportunity to use plant ecology laboratory facilities during a 2 – 4 month research visit to NUI Galway. The project provides a high-level of training in (i) plant biology, plant chemistry and associated laboratory skills; (ii) ecology and palaeoecology; (iii) modelling. The student will be supported throughout the studentship by a comprehensive PGR skills training programme that follows the VITAE Research Development Framework and focuses on knowledge and intellectual abilities; personal effectiveness; research governance and organisation; and engagement, influence and impact. Training needs will be assessed at the beginning of the project and at key stages throughout the project and the student will be encouraged to participate in the numerous training and development course that are run within the university.

Student profile:                                                                                                   The student should have a keen interest in plant biology and palaeoecology with a strong background in a physical geography, Earth sciences, plant sciences, environmental sciences or related discipline. Strong analytical/statistical/fieldwork skills are desirable but not essential, as full training will be provided during the PhD.

References

– Bacon et al., (2016) Can atmospheric composition influence plant fossil preservation via changes in leaf mas per area? A new hypothesis based on simulated palaeoatmosphere experiments. Palaeogeography, Palaeoclimatology, Palaeoecology 464: 51 – 64.

– Bush & McInerney, 2015. Influence of temperature and C4 abundance on n-alkane chain length distributions across the central USA. Organic Geochemistry 79, 65–73.

– Diefendorf et al., 2012. Distribution and carbon isotope patterns of diterpenoids and triterpenoids in modern temperate C3 trees and their geochemical significance. Geochimica et Cosmochimica Acta 85, 342–356.

– Pan et al., 2011. A large and persistent carbon sink in the world’s forests. Science 333, 988 – 993.

– Ryalls et al., 2017. Climate and atmospheric change impacts on sap-feeding herbivores: a mechanistic explanation based on functional groups of primary metabolites. Functional Ecology 31, 161–171.

– Shtein et al., 2018. Plant and algal structure: from cell walls to biomechanical function. Physiologia Plantarum 164, 56 – 66.

– Wright et al., (2004). The worldwide leaf economic spectrum. Nature. 428: 821–827.